Examination

biology essay

"Genetics and human problems"

student of class 11A

Kirov Physics and Mathematics Lyceum

Ponomarev Andrey.

Kirov, 2000.

Plan.

o Introduction 3

o Main stages of development of genetics 3

o Nucleic acids 8

o Genetic code 9

o Protein biosynthesis 10

o Chromosome complex 10

o Human sex chromosomes 11

o Properties of the human genome: mutability 11

o Properties of the human genome: variability 14

o Discrete variability 14

o Continuous variability 15

o Environmental influence 15

o Sources of variability 16

o Hereditary diseases 17

o Hereditary metabolic diseases 28

o Lethal genes 30

o Medical genetic counseling 31

o Genetic monitoring 34

o Conclusion 35

o Used literature 37

Introduction.

Genetics is one of the main, most fascinating and at the same time complex disciplines of modern natural science. The place of genetics among the biological sciences and the special interest in it are determined by the fact that it studies the basic properties of organisms, namely heredity And variability .

As a result of numerous experiments in the field of molecular genetics, brilliant in design and exquisite in execution, modern biology has been enriched by two fundamental discoveries, which have already been widely reflected in human genetics, and were partially carried out on human cells. This shows the inextricable connection between the successes of human genetics and the successes of modern biology, which is becoming more and more connected with genetics.

The first is the ability to work with isolated genes. It was obtained by isolating the gene in its pure form and synthesizing it. The significance of this discovery is difficult to overestimate. It is important to emphasize that different methods are used for gene synthesis, i.e. there is already a choice when it comes to such a complex mechanism as a person.

The second achievement is proof of the inclusion of foreign information in the genome, as well as its functioning in the cells of higher animals and humans. Materials for this discovery accumulated from different experimental approaches. First of all, these are numerous studies in the field of the viral-genetic theory of the emergence of malignant tumors, including the detection of DNA synthesis on an RNA matrix. In addition, experiments with prophage transduction, stimulated by the idea of ​​genetic engineering, confirmed the possibility of the functioning of genes of simple organisms in mammalian cells, including human cells.

Without exaggeration, we can say that, along with molecular genetics, human genetics is one of the most progressive branches of genetics in general. Her research extends from the biochemical to the population level, including the cellular and organismal levels.

But let us consider separately the history of the development of genetics.

The main stages of development of genetics.

The origins of genetics, like any science, should be sought in practice. Genetics arose in connection with the breeding of domestic animals and the cultivation of plants, as well as with the development of medicine. Since man began to use the crossing of animals and plants, he was faced with the fact that the properties and characteristics of the offspring depend on the properties of the parent individuals chosen for crossing. By selecting and crossing the best descendants, man from generation to generation created related groups - lines, and then breeds and varieties with their characteristic hereditary properties.

Although these observations and comparisons could not yet become the basis for the formation of science, the rapid development of animal husbandry and breeding, as well as plant growing and seed production in the second half of the 19th century gave rise to increased interest in the analysis of the phenomenon of heredity.

The development of the science of heredity and variability was especially strongly promoted by Charles Darwin's doctrine of the origin of species, which introduced into biology the historical method of studying the evolution of organisms. Darwin himself put a lot of effort into studying heredity and variability. He collected a huge amount of facts and made a number of correct conclusions based on them, but he was unable to establish the laws of heredity. His contemporaries, the so-called hybridizers, who crossed various forms and looked for the degree of similarity and difference between parents and descendants, were also unable to establish general patterns of inheritance.

Another condition that contributed to the establishment of genetics as a science was advances in the study of the structure and behavior of somatic and germ cells. Back in the 70s of the last century, a number of cytological researchers (Chistyakov in 1972, Strasburger in 1875) discovered the indirect division of somatic cells, called karyokinesis (Schleicher in 1878) or mitosis (Flemming in 1882) . In 1888, at the suggestion of Waldeira, the permanent elements of the cell nucleus were called “chromosomes”. In those same years, Flemming divided the entire cycle of cell division into four main phases: prophase, metaphase, anaphase and telophase.

Simultaneously with the study of somatic cell mitosis, research was carried out on the development of germ cells and the mechanism of fertilization in animals and plants. In 1876, O. Hertwig established for the first time in echinoderms the fusion of the sperm nucleus with the egg nucleus. N.N. Gorozhankin in 1880 and E. Strasburger in 1884 established the same for plants: the first - for gymnosperms, the second - for angiosperms.

In the same year, Van Beneden (1883) and others revealed the cardinal fact that during development, germ cells, unlike somatic cells, undergo a reduction in the number of chromosomes by exactly half, and during fertilization - the fusion of the female and male nuclei - the normal number of chromosomes is restored , constant for each species. Thus, it was shown that each species is characterized by a certain number of chromosomes.

So, the above conditions contributed to the emergence of genetics as a separate biological discipline - a discipline with its own subject and research methods.

The official birth of genetics is considered to be the spring of 1900, when three botanists, independently of each other, in three different countries, at different sites, came to the discovery of some of the most important patterns of inheritance of traits in the offspring of hybrids. G. de Vries (Holland), based on work with evening primrose, poppy, datura and other plants, reported “the law of hybrid splitting”; K. Correns (Germany) established the patterns of segregation in corn and published the article “Gregor Mendel’s Law on the Behavior of Offspring in Racial Hybrids”; in the same year, K. Csermak (Austria) published an article (On artificial crossing in Pisum Sativum).

Science knows almost no unexpected discoveries. The most brilliant discoveries that create stages in its development almost always have their predecessors. This happened with the discovery of the laws of heredity. It turned out that the three botanists who discovered the pattern of segregation in the offspring of intraspecific hybrids merely “rediscovered” the patterns of inheritance discovered back in 1865 by Gregor Mendel and outlined by him in the article “Experiments on plant hybrids,” published in the “proceedings” of the Society of Natural Scientists in Brünn (Czechoslovakia).

Using pea plants, G. Mendel developed methods for genetic analysis of the inheritance of individual traits of an organism and established two fundamentally important phenomena:

1. characteristics are determined by individual hereditary factors that are transmitted through germ cells;

2. individual characteristics of organisms do not disappear during crossing, but are preserved in the offspring in the same form as they were in the parent organisms.

For the theory of evolution, these principles were of cardinal importance. They revealed one of the most important sources of variability, namely the mechanism for maintaining the fitness of the characteristics of a species over a number of generations. If the adaptive characteristics of organisms that arose under the control of selection were absorbed and disappeared during crossing, then the progress of the species would be impossible.

All subsequent development of genetics was associated with the study and expansion of these principles and their application to the theory of evolution and selection.

From the established fundamental principles of Mendel, a number of problems logically follow, which step by step receive their solution as genetics develops. In 1901, de Vries formulated the theory of mutations, which states that the hereditary properties and characteristics of organisms change abruptly - mutationally.

In 1903, the Danish plant physiologist V. Johannsen published the work “On Inheritance in Populations and Pure Lines,” in which it was experimentally established that outwardly similar plants belonging to the same variety are hereditarily different - they constitute a population. A population consists of hereditarily different individuals or related groups - lines. In the same study, it is most clearly established that there are two types of variability in organisms: hereditary, determined by genes, and non-hereditary, determined by a random combination of factors acting on the manifestation of traits.

At the next stage in the development of genetics, it was proven that hereditary forms are associated with chromosomes. The first fact revealing the role of chromosomes in heredity was the proof of the role of chromosomes in determining sex in animals and the discovery of the mechanism of 1:1 sex segregation.

Since 1911, T. Morgan and his colleagues at Columbia University in the USA began to publish a series of works in which he formulated the chromosomal theory of heredity. Experimentally proving that the main carriers of genes are chromosomes, and that genes are located linearly on chromosomes.

In 1922 N.I. Vavilov formulates the law of homological series in hereditary variability, according to which plant and animal species related by origin have similar series of hereditary variability. Applying this law, N.I. Vavilov established the centers of origin of cultivated plants, in which the greatest diversity of hereditary forms is concentrated.

In 1925, in our country G.A. Nadson and G.S. Filippov on mushrooms, and in 1927 G. Möller in the USA on the fruit fly Drosophila obtained evidence of the influence of X-rays on the occurrence of hereditary changes. At the same time, it was shown that the rate of mutations increases by more than 100 times. These studies proved the variability of genes under the influence of environmental factors. Proof of the influence of ionizing radiation on the occurrence of mutations led to the creation of a new branch of genetics - radiation genetics, the importance of which grew even more with the discovery of atomic energy.

In 1934, T. Paynter, using giant chromosomes of the salivary glands of dipterans, proved that the discontinuity of the morphological structure of chromosomes, expressed in the form of various disks, corresponds to the location of genes in chromosomes, previously established by purely genetic methods. This discovery marked the beginning of the study of the structure and functioning of the gene in the cell.

In the period from the 40s to the present time, a number of discoveries (mainly on microorganisms) of completely new genetic phenomena have been made, revealing the possibilities of analyzing gene structure at the molecular level. In recent years, with the introduction of new research methods into genetics, borrowed from microbiology, we have come to the solution to how genes control the sequence of amino acids in a protein molecule.

First of all, it should be said that it has now been fully proven that the carriers of heredity are chromosomes, which consist of a bundle of DNA molecules.

Quite simple experiments were carried out: pure DNA was isolated from killed bacteria of one strain with a special external characteristic and transferred to living bacteria of another strain, after which the reproducing bacteria of the latter acquired the characteristic of the first strain. Numerous similar experiments show that DNA is the carrier of heredity.

In 1953, F. Crick (England) and J. Watstone (USA) deciphered the structure of the DNA molecule. They found that each DNA molecule is composed of two polydeoxyribonucleic chains, spirally twisted around a common axis.

Currently, approaches have been found to solving the problem of organizing the hereditary code and experimentally deciphering it. Genetics, together with biochemistry and biophysics, has come close to elucidating the process of protein synthesis in a cell and the artificial synthesis of protein molecules. This begins a completely new stage in the development of not only genetics, but all biology as a whole.

The development of genetics to this day is a continuously expanding background of research into the functional, morphological and biochemical discreteness of chromosomes. A lot has already been done in this area, a lot has already been done, and every day the cutting edge of science is approaching the goal - unraveling the nature of the gene. To date, a number of phenomena have been established that characterize the nature of the gene. Firstly, a gene on a chromosome has the property of self-reproduction (autoreproduction); secondly, it is capable of mutational change; thirdly, it is associated with a certain chemical structure of deoxyribonucleic acid - DNA; fourthly, it controls the synthesis of amino acids and their sequences in protein molecules. In connection with recent research, a new idea of ​​the gene as a functional system is being formed, and the effect of the gene on determining traits is considered in an integral system of genes - the genotype.

The emerging prospects for the synthesis of living matter attract great attention from geneticists, biochemists, physicists and other specialists.

Nucleic acids.

Nucleic acids, like proteins, are essential for life. They represent the genetic material of all living organisms, down to the simplest viruses. Elucidation of the structure of DNA opened a new era in biology, as it made it possible to understand how living cells accurately reproduce themselves and how they encode the information necessary to regulate their vital functions. Nucleic acids are made up of monomeric units called nucleotides. Long molecules called polynucleotides are built from nucleotides. A nucleotide molecule is made up of three parts: a five-carbon sugar, a nitrogenous base, and a phosphoric acid. The sugar found in nucleotides is pentose.

There are two types of nucleic acids – ribonucleic acids (RNA) and deoxyribonucleic acids (DNA). Both types of nucleic acids contain four different types of bases: two of them belong to the class of purines, the others to the class of pyrimidines. The nitrogen contained in the rings gives the molecules their basic properties. Purines are adenine (A) and guanine (G), and pyrimidines are cytosine (C) and thymine (T) or uracil (U). Purine molecules have two rings, and pyrimidine molecules have one. RNA contains uracil instead of thymine. Thymine is chemically very close to uracil, or more precisely 5-methyluracil.

Nucleic acids are acids because their molecules contain phosphoric acid. When a sugar combines with a base, a nucleoside is formed. The connection occurs with the release of a water molecule. To form a nucleotide, another condensation reaction is required, as a result of which a phosphoester bond is formed between the nucleoside and phosphoric acid. Different nucleotides differ from each other in the nature of the sugars and bases that comprise them. The role of nucleotides in the body is not limited to serving as the building blocks of nucleic acids; some important coenzymes are also nucleotides or their derivatives.

Two nucleotides combine to form a dinucleotide by condensation. As a result, a phosphodiester bridge appears between the phosphate group of one nucleotide and the sugar of another. During the synthesis of polynucleotides, this process is repeated several million times. Phosphodiester bridges arise due to strong covalent bonds, and this imparts strength and stability to the entire nucleotide chain, which is very important, since this reduces the risk of DNA “breakages” during its replication.

RNA has two forms: transfer RNA (tRNA) and ribosomal RNA (rRNA). They have a rather complex structure. The third form is messenger or messenger RNA (mRNA). All these forms are involved in protein synthesis. mRNA is a single-stranded molecule formed on one of the DNA strands during transcription. During mRNA synthesis, only one strand of the DNA molecule is copied. The nucleotides from which mRNA is synthesized are added to DNA in accordance with the rules of base pairing and with the participation of the enzyme RNA polymerase. The sequence of bases in mRNA is a complementary copy of the DNA strand - the template. Its length can vary, depending on the length of the polypeptide chain it encodes. Most mRNA exists in the cell for a short time.

Ribosomal RNA is encoded by special genes located on several chromosomes. The rRNA sequence is similar in all organisms. It is contained in the cytoplasm, where, together with protein molecules, it forms cellular organelles called ribosomes. Protein synthesis occurs on ribosomes. Here, the “code” contained in the mRNA is translated into the amino acid sequence of the polypeptide chain being built. Groups formed by ribosomes - polyribosomes (polysomes) - make it possible for the simultaneous synthesis of several polypeptide molecules with the participation of one mRNA molecule.

For each amino acid there is a specific tRNA, and they all deliver the amino acids contained in the cytoplasm to the ribosomes. Thus, tRNAs play the role of links between the triplet code contained in the mRNA and the amino acid sequence in the polypeptide chain. Since many amino acids are encoded by several triplets, the number of tRNAs is much greater than 20 (60 have already been identified). Each amino acid is attached to one of its tRNAs. As a result, an aminoacyl tRNA is formed, in which the binding energy between the terminal nucleotide A and the amino acid is sufficient for the subsequent formation of a peptide bond with the carboxyl group of the neighboring amino acid.

Genetic code.

The sequence of bases in DNA nucleotides must determine the amino acid sequence of proteins. This relationship between bases and amino acids is the genetic code. Using four types of nucleotides, parameters for the synthesis of protein molecules are written. The code of base triplets includes four different triplets. The proof of the triplet nature of the code was presented by F. Crick in 1961. For many amino acids, only the first letters are significant. One of the features of the genetic code is that it is universal. All living organisms have the same 20 amino acids and five nitrogenous bases.

Currently, advances in molecular biology have reached such a level that it has become possible to determine the sequence of bases in entire genes. This is a major milestone in the development of science, since it is now possible to artificially synthesize entire genes. This has found application in genetic engineering.

Biosynthesis of proteins.

The only molecules that are synthesized under the direct control of the cell's genetic material are proteins (except for RNA). Proteins can be structural (keratin, collagen) or play a functional role (insulin, fibrinogen and, most importantly, enzymes responsible for the regulation of cellular metabolism). It is the set of enzymes contained in a given cell that determines what type of cell it will belong to. In 1961, two French biochemists Jacob and Monod, based on theoretical considerations, postulated the existence of a special form of RNA that plays the role of an intermediary in protein synthesis. This messenger was later named mRNA.

Data obtained using various experimental methods have shown that the process of RNA synthesis consists of two stages. At the first stage (transcription), relatively weak hydrogen bonds between the complementary bases of polynucleotide chains are broken, which leads to the unwinding of the DNA double helix and the release of single strands. One of these strands is selected as a template for the construction of a complementary single strand of mRNA. mRNA molecules are formed as a result of the binding of free ribonucleotides to each other. Synthesized mRNA molecules carrying genetic information leave the nucleus and are sent to ribosomes. After a sufficient number of mRNA molecules have been formed, transcription stops and the two DNA strands in this area are reconnected, restoring the double helix. The second stage is translation, which occurs on ribosomes. Several ribosomes can attach to an mRNA molecule, like beads on a string, forming a structure called a polysome. The advantage of such a complex is that it makes possible the simultaneous synthesis of several polypeptide chains on one mRNA molecule. Once a new amino acid has joined the growing polypeptide chain, the ribosome moves along the mRNA strands. The tRNA molecule leaves the ribosome and returns to the cytoplasm. At the end of translation, the polypeptide chain leaves the ribosome.

Human chromosome complex.

There are no two completely identical people on Earth, with the exception of identical twins. The reasons for this diversity are not difficult to understand from a genetic point of view.

The number of chromosomes in humans is 46 (23 pairs). If we assume that the parents differ in each pair of chromosomes in only one gene, then the total number of possible genotypic combinations is 2 23 . In fact, the number of possible combinations will be much greater, since this calculation does not take into account the crossover between homologous chromosomes. Consequently, from the moment of conception, each person is genetically unique and inimitable.

Human sex chromosomes.

Genes found on sex chromosomes are called sex-linked. The phenomenon of linkage of genes localized on the same chromosome is known as Morgan's law. There is a region on the X chromosome for which there is no homologue on the Y chromosome. Therefore, in a male individual, the characteristics determined by the genes of this region appear even if they are recessive. This special form of linkage helps explain the inheritance of sex-linked traits such as color blindness, early baldness, and hemophilia in humans. Hemophilia is a sex-linked recessive trait in which blood clotting is impaired. The gene that determines this process is located in a region of the X chromosome that does not have a homolog, and is represented by two alleles - a dominant normal and a recessive mutant.

Female individuals who are heterozygous for a recessive or dominant are called carriers of the corresponding recessive gene. They are phenotypically normal, but half of their gametes carry a recessive gene. Despite the father having a normal gene, sons of carrier mothers have a 50% chance of developing hemophilia.

Properties of the human genome: Mutability.

The variability of organisms is one of the main factors of evolution. It serves as the main source for the selection of forms most adapted to living conditions.

Variation is a complex process. Biologists usually divide it into hereditary and non-hereditary. Hereditary variability includes such changes in the characteristics and properties of organisms that do not disappear during sexual reproduction and persist over a number of generations. Non-hereditary variability - modifications, or fluctuations - includes changes in the properties and characteristics of an organism that arise in the process of its individual development under the influence of environmental factors that have developed in a specific way for each individual, and are not preserved during sexual reproduction.

Hereditary variability is a change in the genotype, non-hereditary variability is a change in the phenotype of the organism.

The term "mutation" was first proposed by Hugo de Vries in his classic work "Mutation Theory" (1901 - 1903). He called a mutation the phenomenon of spasmodic, discontinuous changes in a hereditary trait. The main provisions of the theory of G. de Vries have still not lost their significance, and therefore they should be given here:

1) the mutation occurs suddenly, without any transitions;

2) the new forms are completely constant, i.e. stable;

3) mutations, unlike non-hereditary changes (fluctuations), do not form continuous series and are not grouped around an average type (mode). Mutations are qualitative changes;

4) mutations go in different directions, they can be both beneficial and harmful;

5) detection of mutations depends on the number of individuals analyzed to detect mutations.

6) The same mutations can occur repeatedly.

However, G. de Vries made a fundamental mistake by contrasting the theory of mutations with the theory of natural selection. He incorrectly believed that mutations could immediately give rise to new species adapted to the external environment, without the participation of natural selection. In fact, mutations are only a source of hereditary changes that serve as material for natural or artificial selection.

the term “gene” was first used to designate a hereditary trait by Johansen in 1911. The relationship between a gene and a protein, the structure of which is determined by the structure of the gene, was first formulated in the form of the “1 gene - 1 enzyme” hypothesis by Beadle and Tatum. Direct evidence that mutations in a human gene cause changes in the primary structure of proteins was obtained in 1949 by Pauling while studying hereditary hemoglobinopathies. I am studying the primary structure of hemoglobin isolated from the erythrocytes of patients with sickle cell anemia. Pauling showed that the mobility of abnormal hemoglobin in an electric field (electrophoresis) is changed compared to normal. He further found that this effect is associated with the replacement of the amino acid valine with glutamic acid. With this discovery, a new era of discoveries in human biochemical genetics of hereditary metabolic diseases began. They are caused by mutations in genes that produce proteins with abnormal structures, resulting in changes in their functions.

Most organisms store genetic information in DNA - a linear polymer consisting of 4 different monomeric units - deoxyribonucleotides, which are linked together in a chain by phosphodiester bonds. As was proven by Watson and Crick, a typical DNA molecule consists of two plinucleotide chains, each of which contains from several thousand to several million molecules. Each nucleotide in one chain is specifically hydrogen bonded to a nucleotide in the other chain. Only 2 types of nucleotide pairing are found in DNA: deoxyadenosine monophosphate with thymidine monophosphate (A-T pair) and deoxyguanidine monophosphate with deoxycytidine monophosphate (G-C pair). Thus, the nucleotide sequence of one chain precisely determines the sequence in the other, and both chains are complementary to each other. The sequence of four nucleotides along a polynucleotide chain varies among the DNA of unrelated organisms and is the molecular basis of their genetic divergence. Since most hereditary characteristics are transmitted stably from parents to offspring, the sequence of nucleotides in DNA must be exactly copied when an organism reproduces. This occurs in both circuits. The nucleotide sequence and hence the genetic information is conserved during the replication process. Because each nucleotide in the daughter strands is paired specifically with a complementary nucleotide in the parent or template strands before the polymerization process occurs. The DNA of higher organisms is regularly packaged into structures called chromosomes, made up of nucleoprotein elements (nucleosomes). Chromosomes are separated from all other cellular components by the nuclear membrane. Each nucleosomal element is composed of four, sometimes five, protein subunits called histones, which form a core structure around which approximately 140 base pairs of genomic DNA are wound. The structure of histones is highly conserved in the eukaryotic kingdom. The double-stranded DNA model determines the way in which genes can be replicated to be passed on to offspring. The replication process is complex but conceptually simple. The two strands of DNA are separated and each is copied by a series of enzymes that insert complementary bases opposite each base on the original (parent) DNA strand. Thus, two identical double helices are formed from one - this is the process of replication. DNA "makes" RNA, a process called transcription, and RNA "makes" protein, a process called translation. The sequence of the base in a specific gene ultimately dictates the sequence of amino acids in a specific protein; this collinearity between the DNA molecule and the protein is achieved through the genetic code. The four types of DNA bases arranged in groups of three form a triplet, each of which forms a code word, or codon, which determines the inclusion of one amino acid in the structure of the encoded protein, thus determining the inclusion of each of the 20 amino acids that occur in proteins. 64 different triplets exist for 20 amino acids, which determine the properties of the genetic code. Thus, most amino acids are specified by more than one codon, but each codon is completely specific.

Although at present the question of the nature of the gene has not been fully clarified, a number of general patterns of gene mutation have nevertheless been firmly established. Gene mutations occur in all classes and types of animals, higher and lower plants, multicellular and unicellular organisms, bacteria and viruses. Mutational variability as a process of qualitative abrupt changes is universal for all organic forms.

Properties of the human genome: Variability.

Variability is the totality of differences in one or another characteristic between organisms belonging to the same natural population or species. The striking morphological diversity of individuals within any given species attracted the attention of Darwin and Wallace during their travels. The natural, predictable nature of the inheritance of such differences served as the basis for Mendel's research. Darwin established that certain traits can develop as a result of selection, while Mendel explained the mechanism that ensures the transmission from generation to generation of traits for which selection is carried out.

Mendel described how hereditary factors determine the genotype of an organism, which during development is manifested in the structural, physiological and biochemical features of the phenotype. If the phenotypic manifestation of any trait is ultimately determined by the genes that control this trait, then the degree of development of certain traits may be influenced by the environment.

The study of phenotypic differences in any large population shows that there are two forms of variation - discrete and continuous. To study variation in a trait, such as height in humans, it is necessary to measure that trait across a large number of individuals in the population being studied. The measurement results are presented in the form of a histogram reflecting the frequency distribution of various variants of this trait in the population. In Fig. Figure 4 shows typical results obtained from such studies and clearly demonstrates the difference between discrete and continuous variability.

Discrete variability

Some traits are represented by a limited number of variants in a population. In these cases, the differences between individuals are clearly expressed, and there are no intermediate forms; such characteristics include, for example, blood groups in humans, wing length in Drosophila, melanistic and light forms in the birch moth (Biston betularia), primrose column length (Primula) and sex in animals and plants. Traits characterized by discrete variation are usually controlled by one or two major genes, which may have two or more alleles, and environmental conditions have relatively little effect on their phenotypic expression.

Since discrete variability is limited to some clearly defined characteristics, it is also called quality variability, unlike quantitative, or continuous, variability.

Picture 1. Histograms reflecting the frequency distribution in the case of intermittent (A) and non-intermittent (B) variability.

Continuous variability

For many characteristics, the population exhibits a complete series of transitions from one extreme to the other without any breaks. The most striking frozen features are such characteristics as mass (weight), linear dimensions, shape and color of the organism as a whole or its individual parts. The frequency distribution for a trait exhibiting continuous variability corresponds to bell curve. Most members of the population fall into the middle part of the curve, and at its ends, corresponding to the two extreme values ​​of a given trait, there are approximately the same (very small) number of individuals. Traits characterized by continuous variability are caused by the combined influence of many genes (polygenes) and environmental factors. Each of these genes individually has a very small effect on the phenotype, but together they create a significant effect.

Environmental influence

The main factor determining any phenotypic trait is the genotype. The genotype of an organism is determined at the moment of fertilization, but the degree of subsequent expression of this genetic potential depends largely on external factors affecting the organism during its development. For example, the long-stemmed pea variety used by Mendel usually reached a height of 180 cm. However, for this it needed appropriate conditions - lighting, water supply and good soil. In the absence of optimal conditions (if there are limiting factors) the tall stem gene could not fully express its effect. The effect of interaction between genotype and environmental factors was demonstrated by the Danish geneticist Johansen. In a series of experiments on dwarf beans, he selected the heaviest and lightest seeds from each generation of self-pollinating plants and planted them to produce the next generation. Repeating these experiments over several years, he found that within a "heavy" or "light" breeding line, seeds varied little in average weight, while the average weight of seeds from different lines varied greatly. This suggests that the phenotypic manifestation of a trait is influenced by both heredity and environment. Based on these results, continuous phenotypic variation can be defined as “the cumulative effect of varying environmental factors affecting a variable genotype.” In addition, these results show that the degree of heritability of a given trait is determined primarily by the genotype. As for the development of such purely human qualities as individuality, temperament and intelligence, then, judging by the available data, they depend on both hereditary and environmental factors, which, interacting to varying degrees in different individuals, influence the final expression of the trait. It is these differences in these and other factors that create phenotypic differences between individuals. We do not yet have data that would firmly indicate that the influence of some of these factors always predominates, but the environment can never bring the phenotype beyond the limits determined by the genotype.

Sources of Variation

It must be clearly understood that the interaction between discrete and continuous variability and the environment makes it possible for two organisms with an identical phenotype to exist. The mechanism of DNA replication during mitosis is so close to perfection that the possibilities of genetic variability in organisms with asexual reproduction are very small. Therefore, any visible variability in such organisms is almost certainly due to environmental influences. As for organisms that reproduce sexually, there is ample opportunity for genetic differences to arise. Two processes that occur during meiosis provide virtually unlimited sources of genetic variation:

1. Reciprocal gene exchange between chromatase-dump homologous chromosomes, which can occur in prophase 1 of meiosis. It creates new clutch groups, i.e. serves as an important source of genetic recombination of alleles .

2. The orientation of pairs of homologous chromosomes (bivalents) in the equatorial plane of the spindle in metaphase I of meiosis determines the direction in which each member of the pair will move in anaphase I. This orientation is random. During metaphase II, pairs of chromatids are again oriented randomly, and this determines which of the two opposite poles one or another chromosome will go to during anaphase II. Random orientation and subsequent independent segregation of chromosomes make possible a large number of different chromosomal combinations in gametes; this number can be calculated.

The third source of variation in sexual reproduction is that the fusion of male and female gametes, resulting in the union of two haploid sets of chromosomes in the diploid nucleus of the zygote, occurs completely randomly (at least in theory); any male gamete has the potential to fuse with any female gamete.

These three sources of genetic variation provide the constant “shuffling” of genes that underlies genetic changes that occur all the time. The environment influences the whole range of resulting phenotypes, and those best adapted to the environment do well. This leads to changes in allele and genotype frequencies in the population. However, these sources of variation do not produce the major changes in genotype that evolutionary theory requires for the emergence of new species. Such changes occur as a result of mutations.

Hereditary diseases (diagnosis, prevention, treatment)

The well-known general position about the unity of internal and external in the development and existence of normal and sick organisms does not lose its significance in relation to hereditary diseases transmitted from parents to children, no matter how such diseases may seem to be determined in advance by pathological hereditary inclinations. However, this position requires a more detailed analysis, since it is not so unambiguous in relation to various forms of hereditary diseases and at the same time applies to a certain extent to such forms of pathology that seem to be caused only by pathogenic environmental factors. Heredity and environment turn out to be etiological factors or play a role in the pathogenesis of any human disease, but the share of their participation in each disease is different, and the greater the share of one factor, the less of the other. From this point of view, all forms of pathology can be divided into four groups, between which there are no sharp boundaries.

The first group consists of hereditary diseases themselves, in which the etiological role is played by a pathological gene, the role of the environment is to modify only the manifestations of the disease. This group includes monogenically caused diseases (such as, for example, phenylketonuria, hemophilia), as well as chromosomal diseases.

The second group is also hereditary diseases caused by a pathological mutation, but their manifestation requires specific environmental influences. In some cases, such a “manifesting” effect of the environment is very obvious, and with the disappearance of the effect of the environmental factor, clinical manifestations become less pronounced. These are the manifestations of hemoglobin HbS deficiency in its heterozygous carriers with a reduced partial pressure of oxygen. In other cases (for example, with gout), long-term adverse environmental effects (dietary habits) are necessary for the manifestation of a pathological gene.

The third group consists of an overwhelming number of common diseases, especially diseases of mature and old age (hypertension, gastric ulcer, most malignant tumors, etc.). The main etiological factor in their occurrence is the unfavorable influence of the environment, however, the implementation of the effect of the factor depends on the individual genetically determined predisposition of the body, and therefore these diseases are called multifactorial, or diseases with a hereditary predisposition. It should be noted that different diseases with a hereditary predisposition are not the same in the relative role of heredity and environment. Among them, one could distinguish diseases with a weak, moderate and high degree of hereditary predisposition.

The fourth group of diseases are relatively few forms of pathology, in the occurrence of which environmental factors play an exceptional role. Usually this is an extreme environmental factor, against which the body has no means of defense (injuries, especially dangerous infections). Genetic factors in this case play a role in the course of the disease and influence its outcome.

Let's take a closer look at all these four groups.

TO chromosomal diseases include forms of pathology that are clinically expressed by multiple malformations, and as a genetic basis have deviations from the normal content of the amount of chromosomal material in the cells of the body, i.e. caused by genomic or chromosomal mutations.

Most chromosomal diseases are sporadic, arising anew as a result of a genomic (chromosomal) mutation in the gamete of a healthy parent or in the first divisions of the zygote, and not inherited over generations, which is associated with the high mortality of patients in the pre-reproductive period. The phenotypic basis of chromosomal diseases is disorders of early embryonic development. Therefore, pathological changes develop even in the prenatal period of development of the body and either cause the death of the embryo or fetus, or create the main clinical picture of the disease already in the newborn. The role of chromosomal pathology in the prenatal death of embryos or fetuses in humans is great. On average, about 40% of diagnosed spontaneous abortions are caused by chromosomal imbalances. About 6% of all stillbirths have chromosomal changes. Out of 1000 live births, 3-4 have chromosomal diseases. If all cases of multiple malformations among newborns are taken as 100%, then 35-40% will be caused by chromosome abnormalities.

All chromosomal diseases on this basis can be divided into two large groups: caused by a change in the number of chromosomes while maintaining the structure of the latter (genomic mutations) and caused by changes in chromosome structure (chromosomal mutations). All known types of mutations of both types have been described in humans.

Numerical disorders may consist of a change in the ploidy of the chromosome set and a deviation of the number of chromosomes from diploid for each pair of chromosomes towards a decrease (monosomy) or an increase (polysemy). Genomic mutations on individual chromosomes are numerous; they make up the bulk of chromosomal diseases. Complete monosomies are observed on the X chromosome, leading to the development of Shereshevsky-Turner syndrome.

This syndrome develops with complete X-monosomy, when all or most cells have a chromosome set. The clinical manifestations of this syndrome are the absence of usual secondary sexual characteristics in women, short stature, close nipples, skeletal disorders, infertility, and various defects of internal organs.

The most fully studied is trisomy on chromosome 21, or, as it is also called, Down's disease. This anomaly, named after the doctor who first described it in 1866, is not caused by chromosome segregation.

Its symptoms include mental retardation, decreased resistance to disease, congenital cardiac abnormalities, a short stocky body and thick neck, as well as characteristic folds of skin over the inner corners of the eyes, which creates an external resemblance to representatives of the Mongoloid race. Down syndrome and other similar anomalies are more common in children born to older women. The exact reason for this is unknown, but it appears to have something to do with the age of the mother's eggs. The number of X chromosomes in an individual can reach up to 5 while maintaining its viability.

Structural rearrangements of chromosomes, no matter what type they are, cause disturbances in the development of the organism due to or a lack of part of the material on a given chromosome (partial monosomy) or its excess (partial trisomy).

As an example we can give X-polysomy in the absence of the Y chromosome. Such organisms have a chromosome set of 47.XXX, and although outwardly the women look normal and are fertile, they have mental retardation.

With Klinefelter syndrome (47,XXY), a man has some secondary female characteristics, is infertile, the testicles are poorly developed, there is little facial hair, sometimes mammary glands develop, and usually a low level of mental development.

With chromosome set 47.XYU, men are tall, have different levels of mental development, sometimes have psychopathic traits or show a tendency to commit petty crimes.

Gene diseases are divided into two large groups: diseases with an identified primary biochemical defect and diseases with an unclear primary biochemical defect. The first group includes hereditary diseases of metabolism, protein biosynthesis, and enzymes.

An example of hereditary defects in carbohydrate metabolism is galactosemia. One of the pathways for the exchange of monosaccharides in the body is the conversion of 0-galactose, which enters the body with food (formed in the intestine during the enzymatic hydrolysis of food lactose), into 0-glucose. The conversion process consists of several stages and can be interrupted if there is a deficiency of the galactoeo-1 enzyme -phosphateuridyltransferaea. Most often, the mutation leads to insufficient enzyme activity (10-12% of normal levels). The biochemical pathogenesis of the disease includes the accumulation of galactose in various tissues and in the blood, which leads to impaired glucose utilization in the liver, kidneys and brain. Galactosemia occurs among newborns with a frequency of 1 in 35-150 thousand births. The disease develops after birth while feeding the baby, since lactose, a source of non-metabolized galactose, is supplied with milk. As a result, the child experiences vomiting and diarrhea, leading to dehydration, and the gradual development of mental retardation during background of general dystrophy.If, with the help of an appropriate diet, which includes the complete exclusion of milk sugar, the child gets better, later with age a second metabolic pathway appears for the conversion of galactose into glucose - with the participation of the enzyme uridyltransferase.

Hereditary aminoacidopathies (hereditary defects in amino acid metabolism) constitute the largest group of hereditary metabolic defects. By the beginning of 1985, their list included about 60 different nosological units, and although each of them is rare (1:20,000 - 1:100,000 newborns), in total they make up a significant part of hereditary metabolic defects.

Phenylketonuria. Clinically, this disease was first described in 1934, but only 19 years later it was established that this hereditary defect is associated with a deficiency of phenylalanine-4-hydroxylase. Normally, excess phenylalanine received from food and not used for protein synthesis is converted into tyrosine with the help of this enzyme. In patients with phenylketonuria, this amino acid accumulates in the blood. Elevated levels of phenylalanine are not dangerous in themselves, but they do stimulate unusual reactions that cause keto derivatives of phenylalanine to accumulate in the body. They cause damage to nervous tissue in newborns and the development of mental retardation in the future. Therefore, if the presence of this disease is detected in time and phenylalanine is excluded from food, the child will develop normally. There are several methods for diagnosing phenylketonuria. Microbiological tests are the most widely used.

Vitamins act as cofactors, prosthetic groups, and many enzymes. Insufficient intake from food sharply reduces the activity of the corresponding metabolic processes. The resulting diseases are called vitamin deficiency and are easily treated by introducing the missing vitamins into the body. However, there are vitamin-independent vitamin deficiencies in which such measures have no effect. The causes of such diseases, which are usually hereditary, were discovered after careful study of vitamin metabolism. Before acting as a coenzyme, the vitamin must be extracted from the intestines by special transport proteins and transported into the bloodstream. There it undergoes enzymatic modification and only then can it contact the apoenzyme (if its structure is not changed), turning it into an active enzyme. Each of the genes encoding proteins responsible for these transformations can be inactivated by the corresponding mutation. These genetic disorders give rise to diseases, for the treatment of which it is necessary to introduce ready-made coenzymes into the body. The development of treatment methods should be based on accurate knowledge of the metabolic pathways of this vitamin. The most difficult situation occurs when the apoenzyme is damaged. There are currently no effective ways to cope with this pathology.

An example of hereditary defects in circulating proteins is sickle cell anemia. The protein part of any human hemoglobins (Hb) consists of two globin chains, each built from two polypeptide chains. Human hemoglobin is made up of two alpha and two beta chains. In sickle cell anemia, valine at the beta position is replaced by glutalic acid. This replacement causes reduced hemoglobin solubility. Heterozygous carriers of HbS are clinically healthy under normal conditions, since the blood also contains normal HbA; the anomaly begins to manifest itself only in conditions of low pressure (in the mountains). Homozygotes from an early age develop a characteristic picture of chronic anemia with circulatory disorders and thrombosis. Hemoglobin HbS is often found in the population of regions where malaria is common, since it is insensitive to Plasmodium falciparum.

An example of a hereditary disease with an unknown primary biochemical defect is achondroplasia. It is an example of a hereditary disease with a firmly established dominant mode of inheritance. However, due to the sharply reduced ability of patients to have offspring, in almost 80-95% of cases this disease is associated with new emerging mutations.

Achondroplaeia is one of the hereditary diseases of the skeletal system; its clinical picture is caused by abnormal growth and development of cartilage tissue, mainly in the epiphyses of tubular bones and the base of the skull. Nothing is known about the biochemical nature of this disease, except for information about various deviations in the activity of a number of enzymes, the significance of which remains unclear.

The pathology of the growth of these bones determines the characteristic clinical picture, which is completely resolved in patients of puberty: 1) short stature (usually up to 120 cm) while maintaining normal body length; 2) macrocephaly, tuberous brain part of the skull and a characteristic face; 3) sharp shortening of the upper and lower extremities, especially due to the femur and humerus, with their deformation and thickening.

Schizophrenia is a multifactorial disease, or a disease with a hereditary predisposition. It occupies a leading place in frequency among endogenous functional psychoses (more than 1%). The familial nature of the incidence of schizophrenia and the participation of hereditary factors in its etiology have long been beyond doubt, however, as for other diseases with a hereditary predisposition, the genetic nature of the predisposition remains not fully deciphered. In recent years, the genetic patterns of schizophrenia have been actively studied by Soviet researchers under the leadership of M. E. Vartanyan, and these studies continue to this day.

As has already been emphasized, with the development of medicine, hereditary diseases make up an increasing proportion of the general pathology of humans. Most hereditary diseases have a chronic course, as a result of which the repeated appeal of such patients is high. At the same time, as an analysis of the patient population shows, hereditary forms are not always diagnosed even in clinical settings. To a certain extent, this is understandable, since diagnosing hereditary pathology is a very complex and labor-intensive process.

Difficulties in diagnosis are due primarily to the fact that nosological forms of hereditary diseases are very diverse (about 2000) and each of them is characterized by a wide variety of clinical pictures. Thus, in the group of nervous diseases, more than 200 hereditary forms are known, and in dermatology there are more than 250 of them. Some forms are extremely rare, and a doctor may not encounter them in his practice. Therefore, he must know the basic principles that will help him suspect rare hereditary diseases, and after additional consultations and examinations, make an accurate diagnosis.

Diagnosis of hereditary diseases is based on data from clinical, paraclinical and special genetic examinations.

During a general clinical examination of any patient, the diagnosis should result in one of three conclusions:

1. a clear diagnosis of a non-hereditary disease has been made;

2. a hereditary disease has been clearly diagnosed;

3. there is a suspicion that the underlying or concomitant disease is hereditary.

The first two conclusions make up the overwhelming majority when examining patients. The third conclusion, as a rule, requires the use of special additional examination methods, which are determined by a geneticist.

A complete clinical examination, including paraclinical examination, is usually sufficient to diagnose a hereditary disease such as achondroplaeia.

In cases where the patient has not been diagnosed and it is necessary to clarify it, especially if a hereditary pathology is suspected, the following special methods are used:

1. A detailed clinical and genealogical examination is carried out in all cases when, during the initial clinical examination, a suspicion of a hereditary disease arises. It should be emphasized here that we are talking about a detailed examination of family members. This examination ends with a genetic analysis of its results.

2. Cytogenetic research can be carried out on parents, sometimes on other relatives and the fetus. The chromosome set is studied when a chromosomal disease is suspected to clarify the diagnosis. A major role of cytogenetic analysis is prenatal diagnosis.

3. Biochemical methods are widely used in cases where there is a suspicion of hereditary metabolic diseases, those forms of hereditary diseases in which a defect in the primary gene product or a pathogenetic link in the development of the disease has been accurately established.

4. Immunogenetic methods are used to examine patients and their relatives in cases of suspected immunodeficiency diseases, in cases of suspected antigenic incompatibility of mother and fetus, in establishing true parenthood in cases of medical genetic counseling, or to determine hereditary predisposition to diseases.

5. Cytological methods are used to diagnose a still small group of hereditary diseases, although their capabilities are quite large. Cells from patients can be examined directly or after cultivation using cytochemical, autoradiographic and other methods.

6. The gene linkage method is used in cases where there is a case of the disease in the pedigree and it is necessary to decide whether the patient has inherited a mutant gene. This is necessary to know in cases of an erased picture of the disease or its late manifestation.

For a long time, the diagnosis of a hereditary disease remained as a sentence of doom for the patient and his family. Despite the successful deciphering of the formal genetics of many hereditary diseases, their treatment remained only symptomatic. For the first time, S. N. Davidenkov, back in the 30s, pointed out the fallacy of the point of view about the incurability of hereditary diseases. It is based on the recognition of the role of environmental factors in the manifestation of hereditary pathology. However, the lack of information about the pathogenetic mechanisms of disease development at that time limited the possibilities of developing methods, and all attempts, despite the correct theoretical principles, remained empirical for a long time. Currently, thanks to the successes of genetics in general (all its branches) and the significant progress of theoretical and clinical medicine, it can be argued that many hereditary diseases are already being successfully treated. General approaches to the treatment of hereditary diseases remain the same as approaches to the treatment of diseases of other origins. Here we can distinguish three approaches: symptomatic, pathogenic, etiological.

Symptomatic treatment used for all hereditary diseases, even where there are methods of pathogenic therapy. For many forms of pathology, symptomatic treatment is the only treatment.

Drug symptomatic therapy is the most commonly used technique, varied depending on the forms of hereditary diseases: the use of analgin for hereditary forms of migraine, specific tranquilizers for mental illnesses, pilocarpine for glaucoma, special ointments for skin diseases, etc. The successes of this section of therapy are associated with the progress of pharmacology, providing an ever wider choice of drugs. On the other hand, deciphering the pathogenesis of each disease allows us to understand the cause of symptoms, and on this basis, drug correction of symptoms becomes more subtle. An example is the symptomatic treatment of cystic fibrosis.

When it was found that with cystic fibrosis, very thick mucus is formed in the ducts of the endocrine glands of the bronchi, then to alleviate the condition, such patients began to be prescribed substances that thin the mucus (mucolytic substances).

Surgical symptomatic treatment occupies an essential place in the treatment of hereditary pathology, especially expressed in the form of congenital malformations or systemic skeletal lesions. For example, blood transfusions for thalassemia, plastic surgery for cleft lip, cataract removal are all examples of symptomatic treatment.

In general terms, types of surgical care for patients with hereditary pathology can be of three types: removal (of tumors, etc.); correction (cleft lip, congenital heart defects, etc.); transplantation (combined immune deficiency, etc.).

In some cases, surgical care goes beyond symptomatic treatment, approaching pathogenetic in nature.

Many types of physical treatment methods (heat therapy, various types of electrotherapy, etc.) are used for hereditary diseases of the nervous system, hereditary metabolic diseases, and skeletal diseases. Symptomatic treatment can also include X-ray and radiological irradiation for hereditary tumors before and after surgery.

The possibilities of symptomatic treatment for many diseases are far from being exhausted, especially in the field of medicinal, dietary and surgical care.

Treatment of many diseases based on the principle of intervention in pathogenesis of diseases always more effective than symptomatic. However, it should be understood that none of the currently existing methods eliminates the cause of the disease, since it does not restore the structure of damaged genes. The action of each of them lasts a relatively short time, so treatment must be continuous. In addition, we have to admit the limitations of modern medicine: many hereditary diseases cannot be effectively treated. In this regard, particular hopes are placed on the use of genetic engineering methods to introduce normal, unchanged genes into the cells of a sick person. In this way it will be possible to achieve a radical cure for this patient, but this is a matter for the future.

Currently, there are the following main directions of therapy for hereditary diseases.

1. Complete or partial removal from food of a substrate or substrate precursor of a blocked metabolic reaction. This technique is used in cases where excessive accumulation of substrate has a toxic effect on the body. Sometimes (especially when the substrate is not vital and can be synthesized in sufficient quantities by roundabout routes) such diet therapy has a very good effect. A typical example is galactosemia. The situation is somewhat more complicated with phenylketonuria. Phenylalanine is an essential amino acid, so it cannot be completely excluded from food, but the minimum required dose of phenylalanine must be individually selected for the patient.

2. Replenishment of cofactors from outside in order to increase enzyme activity. Most often we are talking about vitamins. Their additional administration to a patient with a hereditary pathology gives a positive effect when the mutation disrupts the ability of the enzyme to combine with the activated form of the vitamin in vitamin-sensitive hereditary vitamin deficiencies.

3. Neutralization and elimination of excretion of toxic products that accumulate if their further metabolism is blocked. Such products include, for example, copper for Wilson-Konovalov disease. To neutralize copper, the patient is administered penicillamine.

4. Artificial introduction into the patient’s body of a product of a blocked reaction. For example, taking cytidylic acid for orotoaciduria (a disease in which the synthesis of pyrimidines is affected) eliminates the phenomena of megaloblastic anemia.

5. Impact on “spoiled” molecules. This method is used to treat sickle cell anemia and is aimed at reducing the likelihood of the formation of hemoglobin 3 crystals. Acetylsalicylic acid enhances the acetylation of HbS and thus reduces its hydrophobicity, which causes aggregation of this protein.

6. Administration of the missing hormone or enzyme. This method was originally developed and is still successfully used to treat diabetes by introducing insulin into the patient’s body. Later, other hormones were used for similar purposes. The use of enzyme replacement therapy, however, despite all its attractiveness, encounters a number of difficulties: 1) not in all cases there is a way to deliver the enzyme to the desired cells and at the same time protect it from degradation; 2) if the synthesis of one’s own enzyme is completely suppressed, the exogenous enzyme is inactivated by the patient’s immune system during long-term administration; 3) obtaining and purifying sufficient quantities of enzymes is often a difficult task in itself.

7. Blocking the pathological activity of enzymes using specific inhibitors or competitive inhibition by analogues of the substrates of a given enzyme. This treatment method is used for excessive activation of blood coagulation systems, fibrinolysis, as well as for the release of lysosomal enzymes from destroyed cells.

A comparison of the molecular mechanisms affected by hereditary diseases with the therapeutic methods used to treat them shows that not all the main symptoms of genetically determined human diseases can currently be eliminated. It is hoped that further study of the molecular processes underlying hereditary diseases will in the future lead to a significant expansion of the arsenal of treatment methods.

Despite the successes of symptomatic and pathogenetic treatment of hereditary diseases, the question of the possibility of their etiological treatment remains. And the greater the progress of theoretical biology, the more often the question of radical, i.e. etiological, treatment of hereditary diseases will be raised.

Etiological treatment of any hereditary diseases is the most optimal, since it eliminates the root cause of the disease and completely cures it. However, eliminating the cause of a hereditary disease means such serious “maneuvering” with genetic information in a living human body, such as “turning on” a normal gene (or adding it), “turning off” a mutant gene, or reverse mutation of a pathological allele. These tasks are quite difficult even for manipulating prokaryotes. In addition, in order to carry out etiological treatment of any hereditary disease, it is necessary to change the DNA structure not in one cell, but in all functioning cells (and only functioning ones!). First of all, for this you need to know what change in DNA occurred during the mutation, i.e. hereditary disease must be written down in chemical formulas. The difficulties of this task are obvious, although methods for solving them are already available at the present time.

A schematic diagram for the etiological treatment of hereditary diseases has been drawn up. For example, in case of hereditary diseases accompanied by a lack of enzyme activity (albinism, phenylketonuria), it is necessary to synthesize this gene and introduce it into the cells of a functioning organ. The choice of methods for gene synthesis and its delivery to the appropriate cells is wide, and they will be expanded with the progress of medicine and biology. At the same time, it is necessary to note the importance of exercising great caution when applying methods (precisely during application, and not during development?) of genetic engineering for the treatment of hereditary diseases, even if decisive breakthroughs are made in the synthesis of the corresponding genes and methods of their delivery to target cells. Human genetics does not yet have sufficient information about all the features of the functioning of the human genetic apparatus. It is not yet known how it will work after introducing additional genetic information. There are also other unresolved issues that do not allow us to assume the rapid application of methods for the etiological treatment of hereditary diseases.

Prevention Hereditary pathology in general is undoubtedly the most important branch of modern medicine and healthcare organization. We are talking not just about preventing, as a rule, a serious illness in a particular individual, but also in all his subsequent generations. It is precisely because of this feature of hereditary pathology, which persists from generation to generation, that prevention methods have been proposed more than once in the past, based on eugenic approaches in some cases more humane, in others less. Only the progress of medical genetics has fundamentally changed approaches to the prevention of hereditary pathology; the path has passed from proposals for sterilization of spouses or categorical recommendations of abstinence from childbearing to prenatal diagnosis, preventive treatment (treatment of healthy carriers of pathological genes, preventing the development of the disease) and an individually adaptive environment for carriers of pathological genes.

Hereditary metabolic diseases.

One of the manifestations of an unprecedented breakthrough in the accumulation of medical and genetic information in the second half of the 20th century. was the discovery of a large number of new hereditary metabolic diseases (NBD) with an approximate rate of 100 new units per 10 years. The speed of their discovery, pronounced genetic heterogeneity, clinical polymorphism, and the low frequency of most of them make it extremely difficult for clinicians to utilize this information in their diagnostic practice; the clinical manifestations of NBO are so diverse that there is no medical specialization that does not deal with its own specific spectrum of NBO. Meanwhile, in domestic medicine today there is no modern guidance on this broad class of diseases; NBOs are not only diseases (mostly very severe ones) that require solving the entire complex of medical problems - diagnosis, treatment, prevention. They are also unique biological models of natural metabolic errors, which are an invaluable tool for understanding the complex normal human metabolism. It is on these models that in recent decades the role - both physiological and pathological - of a huge number of metabolites has been clarified, multiple connections between metabolic pathways have been established, and many metabolic pathways have been deciphered or clarified.

According to modern concepts of medical genetics, hereditary diseases of human metabolism (synonym - “molecular diseases”) include a large class of monogenically inherited diseases caused by mutations of structural genes, under the control of which the synthesis of proteins is carried out, performing various functions: structural, transport, enzyme catalysis, immune protection. Based on the fact that by 1988, about 4,500 monogenic human diseases were known (McCusick catalog), and the primary biochemical defect for the first NBO (methemoglobinemia) was deciphered only in 1946 and in 1952 for the second (glucose-6-phosphatase deficiency in Gierke's disease), it is obvious that the study of NBO is a rapidly developing branch of modern medical genetics. At the organismal level of NBO research, the object of study is the clinical and biochemical phenotype of the patient, at the cellular level - mutant proteins, at the molecular level - mutant genes.

Studies of evolution and polymorphism at the molecular level over the past 20 years have shown that mutations can accumulate in populations if their selective disadvantages are small relative to the frequency of the mutation.

The frequency and spectrum of mutant alleles for each gene in populations is influenced by the following factors: mutation frequency, natural selection, genetic drift, migration. For the first of these factors, no interpopulation differences have been identified and it is difficult to assume their existence. As for the other three factors, their influence on the gene pool of different populations is extremely uneven. The existence of geographical, linguistic, tribal, national and other barriers contributed to the subdivision of the world's population and the formation of regional characteristics of the burden of hereditary pathology, which affected the frequency and spectrum of NBO. For those HBO. whose prevalence has been assessed using fairly reliable methods, it has been shown that NBOs are characterized by a pronounced unevenness in their ethnic distribution, which is manifested at both the gene and allelic levels. It should be emphasized that currently the prevalence of most NBOs is either not estimated or estimated approximately. This is due to a number of reasons: the properties of NBO. complicating their clinical diagnosis, the absence or high cost of methodological approaches and organizational difficulties. A number of organizational and methodological approaches to assessing the prevalence of NBO have been developed, which can be divided into indirect and direct.

Accurate estimates of the prevalence of NBO (direct) were obtained using mass screening; mass screening of newborns made it possible to accurately determine the frequency of phenylketonuria, adrenogenital syndrome (21-hydroxylase deficiency), and galactosemia. a number of aminoacidopathies, etc. in a large number of regions of the world predominantly with a Caucasian population (the exception is Japan). Another approach to assessing the prevalence of NBO is a prospective screening program (a type of mass screening) to identify heterozygous carriers of certain incurable lethal or sublethal NBO using biochemical methods. common with high frequency in a number of populations. Thus, the frequency of Tay-Sachs disease in Ashkenazi Jews in many countries of the world and a number of hemoglobinopathies in the countries of the Mediterranean region and immigrants from them in England and the USA were assessed. In a number of countries, newborn capillary blood samples obtained for mass screening have been used to estimate the incidence of NBO, for which mass screening has not been established. A comparison of frequencies between populations, between regions of the same population, and between populations of the same race revealed a large difference in the distribution of frequencies of mutant genes. The uniqueness of genetic-automatic processes and the peculiarities of the historical development of individual populations apparently explain this interesting phenomenon. Attempts have been made in the literature to explain the decreasing gradient of phenylketonuria frequencies in Northern countries. Europe - from Ireland to Finland - the Celtic origin of the mutant allele and associate its spread with the Viking raids.

Lethal genes

There are cases where one gene can influence several traits, including viability. In humans and other mammals, a certain recessive gene causes the formation of internal lung adhesions, leading to death at birth. Another example is a gene that affects the formation of cartilage and causes congenital deformities leading to death of the fetus or newborn.

In chickens homozygous for the allele causing feather curl, incomplete feather development has several phenotypic effects. These chickens have insufficient thermal insulation and suffer from chilling. To compensate for heat loss, they develop a number of structural and physiological adaptations, but these adaptations are ineffective and mortality is high among such chickens.

The effect of a lethal gene is clearly seen in the inheritance of coat color in mice. Wild mice usually have gray fur, like an agouti; but some mice have yellow fur. Crosses between yellow mice produce both yellow mice and agouti in a 2:1 ratio. The only possible explanation for these results is that yellow coat color is dominant in agoutis and that all yellow mice are heterozygous. Atypical Mendelian relationship explained by death homozygous yellow mice before birth. Necropsies on pregnant yellow mice crossed with yellow mice revealed dead yellow pups in their uteruses. If yellow mice and agoutis were crossed, then there were no dead yellow mice in the uteri of pregnant females, since with such a crossing there cannot be offspring homozygous for the yellow wool gene .

Medical genetic counseling.

The most common and effective approach to the prevention of hereditary diseases is medical genetic consultation. From the point of view of healthcare organization, medical genetic counseling is one of the types of specialized medical care. The essence of the consultation is as follows: 1) determining the prognosis for the birth of a child with a hereditary disease; 2) an explanation of the likelihood of this event to those consulting; 3) helping the family make a decision.

If there is a high probability of having a sick child, two recommendations may be correct from a preventive point of view: either abstinence from childbearing, or prenatal diagnosis, if possible for a given nosological form.

The first office for medical genetic counseling was organized in 1941 by J. Neal at the University of Michigan (USA). Moreover, back in the late 50s, the largest Soviet geneticist and neuropathologist S. K. Davidenkov organized a medical-genetic consultation at the Institute of Neuropsychiatric Prevention in Moscow. Currently, there are about a thousand genetic consultations all over the world, and there are 80 in Russia.

The main reason that makes people turn to a geneticist is the desire to find out the prognosis of the future offspring regarding hereditary pathology. As a rule, families are consulted where there is a child with a hereditary or congenital disease (retrospective consultation) or its appearance is expected (prospective consultation) due to the presence of hereditary diseases in relatives, consanguineous marriage, the age of the parents (over 35-40 years), radiation and other reasons.

The effectiveness of a consultation as a medical opinion depends mainly on three factors: the accuracy of the diagnosis, the accuracy of the genetic risk calculation, and the level of understanding of the genetic report by those consulting. There are essentially three stages of counseling.

First stage counseling always begins with clarifying the diagnosis of a hereditary disease. An accurate diagnosis is a necessary prerequisite for any consultation. It depends on the thoroughness of clinical and genealogical research, on knowledge of the latest data on hereditary pathology, on special studies (cytogenic, biochemical, electrophysiological, gene linkage, etc.).

Genealogical research is one of the main methods in the practice of medical genetic counseling. All studies must be supported by documentation. Information is obtained from at least three generations of relatives in the ascending and lateral lines, and data must be obtained on all family members, including those who died early.

During the genealogical research, it may be necessary to refer the subject or his relatives for additional clinical examination in order to clarify the diagnosis.

The need for constant acquaintance with new literature on hereditary pathology and genetics is dictated by diagnostic needs (several hundred new genetic variations, including anomalies, are discovered every year) and preventive ones in order to select the most modern methods of prenatal diagnosis or treatment.

Cytogenetic study applied in at least half of the consulted cases. This is due to the assessment of the prognosis of the offspring with an established diagnosis of a chromosomal disease and to clarify the diagnosis in unclear cases of congenital malformations.

Biochemical, immunological and other clinical methods are not specific to genetic consultation, but are used as widely as in the diagnosis of non-hereditary diseases.

Second phase counseling - determining the prognosis of the offspring. Genetic risk is determined in two ways: 1) through theoretical calculations based on genetic patterns using methods of genetic analysis and variation statistics; 2) using empirical data for multifactorial and chromosomal diseases, as well as for diseases with an unclear mechanism of genetic determination. In some cases, both principles are combined, that is, theoretical amendments are made to the empirical data. The essence of genetic prognosis is to assess the likelihood of the occurrence of hereditary pathology in future or already born children. Consultation on the prognosis of offspring, as mentioned above, is of two types: prospective and retrospective.

Prospective Consulting - this is the most effective type of prevention of hereditary diseases, when the risk of having a sick child is determined before pregnancy or in its early stages. Most often, such consultations are carried out in the following cases: if there is a blood relationship between the spouses; when there were cases of hereditary pathology on the side of the husband or wife; when one of the spouses is exposed to harmful environmental factors shortly before pregnancy or in its first weeks (therapeutic or diagnostic radiation, severe infections, etc.)

retrospective consultation - this is counseling after the birth of a sick child in a family regarding the health of future children. These are the most common reasons for seeking consultation.

Methodologically, determining the prognosis of offspring for diseases with different types of inheritance varies. If for monogenic (Mendelian) diseases the theoretical basis for assessing genetic risk is quite clearly developed, then for polygenic diseases, and especially multifactorial ones, counseling is often based on pure empiricism, reflecting insufficient genetic knowledge of this pathology.

In Mendelian diseases, the task mainly comes down to laboratory identification or probabilistic assessment in those consulting of a certain discrete genotype underlying the disease.

In non-Mendelian diseases, it is currently impossible to identify specific and discrete pathological genotypes that determine the development of the disease, since many genetic and environmental factors that are nonspecific in their effects can participate in its formation, i.e. the same effect (disease) can be caused different genes and/or environmental factors. This creates numerous difficulties in the genetic analysis of non-Mendelian traits and diseases.

Third stage of consultation is final. After diagnosing the subject, examining relatives, and solving the genetic problem of determining genetic risk, the geneticist explains to the family in an accessible form the meaning of genetic risk or the essence of prenatal diagnosis and helps them make a decision.

It is generally accepted that a specific genetic risk of up to 5% is low, up to 10% is mildly increased, up to 20% is moderate, and above 20% is high. You can neglect the risk, which does not go beyond the increased to a mild degree, and do not consider it a contraindication to further childbearing. Only a moderate genetic risk is regarded as a contraindication to conception or as an indication to terminate an existing pregnancy if the family does not want to be at risk.

From a social point of view, the goal of genetic counseling in general is to reduce the frequency of pathological genes in human populations, and the goal of a specific consultation is to help the family decide on the possibility of childbearing. With the widespread introduction of genetic counseling, a slight reduction in the incidence of hereditary diseases, as well as mortality, especially in childhood, can be achieved. However, the reduction in the frequency of severe dominant diseases in populations as a result of medical genetic counseling will not be significant, because 80-90% of them are new mutations.

The effectiveness of medical genetic counseling depends on the degree to which those consulted understand the information they received. It also depends on the nature of the legal laws in the country relating to termination of pregnancy, social security of patients, etc.

Genetic monitoring.

Pollution of the natural environment with harmful industrial waste, products of incomplete combustion, pesticides and other mutagens, an increase in the background of ionizing radiation caused by atomic weapons tests, uncontrolled use of chemicals and radioactive substances in the energy sector, industry, and agriculture - all this leads to a significant increase in genetic disorders.

The genetic burden of these genetic disorders, which undermine the hereditary health of the population, is growing. So in the USSR, since 1980, 200,000 children were born with serious genetic defects and about 30,000 were dead. About 25% of pregnancies are not carried to term due to genetic reasons. Currently, 10% of the total population has a mental disorder. The number of cancer diseases is also increasing. And at the same time, in most cases, diseases are associated with environmental pollution. According to WHO, 80% of diseases are caused by environmental stress. Therefore, problems of genetics, ecology and human adaptation become especially acute.

The most appropriate solution at the moment for solving human ecology problems is the use of environmental monitoring and the social and labor potential of people. The purpose of monitoring is to identify physical, chemical, biological pollution of the environment. Environmental monitoring is carried out on the basis of assessing the health patterns of the population in various territorial production complexes. At the same time, the obtained statistical data cannot be considered absolutely accurate, since they can only indicate an increase in diseases. The lack of clear health criteria and effective means of assessing it also hinders. Undoubtedly, environmental monitoring, as well as other methods of solving environmental problems, one way or another affect genetics. Meanwhile, genetic pollution of our planet is more dangerous than all others. It becomes necessary to predict changes in disease growth. Therefore, genetic monitoring is of particular importance, making it possible to control the mutation process in humans, to identify and prevent all the possibility of genetic danger associated with as yet undetected mutagens.

At the moment, however, mutation studies are difficult to implement.

The difficulties encountered in studying mutations are primarily related to the problem of detecting them in the human body. This is the case, for example, with the registration of a recessive anomaly, since such a mutant gene appears in the body in a homozygous state, which takes some time to achieve. The situation is much simpler with the registration of dominant gene and chromosomal mutations, especially if their appearance in the phenotype is easily detectable.

Thanks to bioecological monitoring through the typification of climatic-geographical and production areas according to health structures (that is, according to the relationships between groups with different levels of health), it is possible to more effectively improve environmental conditions, as well as increase the level of public health. Although a large number of problems remain. For example, indicators of fertility, morbidity and mortality “respond” to environmental changes rather inertly, and only the consequences of environmental troubles are revealed, which does not make it possible to promptly manage the environmental situation.

A number of necessary economic mechanisms to stimulate environmental protection measures have not yet been developed. Although genetic monitoring is a complex matter, it is simply necessary to solve human environmental problems, as well as reduce the growth of diseases, including hereditary ones.

Conclusion.

Genetics is a relatively young science. But she faces very serious problems for humans. Thus, genetics is very important for solving many medical issues related primarily to various hereditary diseases of the nervous system (epilepsy, schizophrenia), endocrine system (cretinism), blood (hemophilia, some anemia), as well as the existence of a number of severe defects in the human structure: short-toed, muscle atrophy and others. With the help of the latest cytological methods, cytogenetic in particular, extensive research is carried out into the genetic causes of various diseases, thanks to which there is a new branch of medicine - medical cytogenetics.

Branches of genetics related to the study of the effect of mutagens on cells (such as radiation genetics) are directly related to preventive medicine.

Genetics began to play a special role in the pharmaceutical industry with the development of microbial genetics and genetic engineering. Undoubtedly, much remains unexplored, for example, the process of mutations or the causes of malignant tumors. It is precisely its importance for solving many human problems that causes the urgent need for the further development of genetics. Moreover, each person is responsible for the hereditary well-being of his children, and an important factor is his biological education, since knowledge in the field of anomalies, physiology, and genetics will prevent a person from making mistakes.

References.

1. A.O. Ruvinsky “Hereditary variability of man”
2. Yu.Ya. Kerkis “Treatment and prevention of certain hereditary human diseases”
3. D.K. Belyayav "General Biology"
4. N. Green, W. Stout “Biology”
5. S. Kotov “Medical Genetics”
6. M.D. Frank-Kamenetsky “The most important molecule”

Basic problems of genetics and the mechanism of life reproduction
Content

Introduction

Chapter 1. The subject of genetics

1.1. Modern ideas about the gene

1.2. Gene structure

1.3. Basic concepts and methods of genetics

Chapter 2. Heredity

2.1. Mendel's studies

2.2. Inheritance in monohybrid crosses and the law of segregation

2.3. Reciprocal or testing crossbreeding

2.4. Dihybrid crossing and the law of independent distribution

2.5. Brief summary of the essence of Mendel's hypotheses

2.6. Clutch

2.7. Determination of gender

2.8. Sex-linked inheritance

2.9. Incomplete dominance

2.10. Variability

2.11. Environmental influence

2.12. Sources of Variation

2.13. Mutations

2.14. Gene mutations

2.15. Lethal mutations

2.16. The meaning of mutations

Chapter 3. Modern capabilities and achievements of genetics and genetic engineering

3.1. Chimeras

3.2. Transgenic organisms

3.3. A little about cloning

3.4. Treatment and prevention of some hereditary human diseases

3.5. Medical genetic counseling

Conclusion

Literature

Introduction

Genetics can rightfully be considered one of the most important areas of biology. For thousands of years, people have used genetic methods to improve the beneficial properties of cultivated plants and breed highly productive breeds of domestic animals, without having any understanding of the mechanisms underlying these methods. Judging by a variety of archaeological evidence, already 6,000 years ago people understood that certain physical characteristics could be passed on from one generation to the next. By selecting certain organisms from natural populations and crossing them with each other, man created improved varieties of plants and breeds of animals that had the properties he needed.

However, only at the beginning of the CC century did scientists begin to fully understand the importance of the laws of heredity and its mechanisms. Although the success of microscopy made it possible to establish that hereditary characteristics are transmitted from generation to generation through sperm and eggs, it remained unclear how the smallest particles of protoplasm could carry the “makings” of that huge variety of characteristics that make up each individual organism.

Genetics took shape as a science after the rediscovery of Mendel's laws. The spring of 1953 became a memorable date in biology. Researchers American D. Watson and Englishman F. Crick deciphered the “holy of holies” of heredity - its genetic code. It was from that time that the word “DNA” - deoxyribonucleic acid - became known not only to a narrow circle of scientists, but also to every educated person around the world. The turbulent century-long period of its development has been marked in recent years by the deciphering of the nucleotide composition of the “molecule of life” DNA in dozens of species of viruses, bacteria, fungi and multicellular organisms. Sequencing (establishing the order of alternation of nucleotides) of the DNA chromosomes of important crop plants - rice, corn, wheat - is in full swing. At the beginning of 2001, the fundamental decoding of the entire human genome was solemnly announced - the DNA that is part of all 23 pairs of chromosomes of the cell nucleus. These biotechnological advances have been compared to going into space.

Deoxyribonucleic acid, or DNA (Figure 1), was first isolated from cell nuclei. That's why it was called nucleic (Greek nucleus - core). DNA is made up of a chain of nucleotides with four different bases: adenine (A), guanine (G), cytosine (C) and thymine (T). DNA almost always exists as a double helix, meaning it consists of two nucleotide chains that form a pair. They are held together by so-called base pair complementarity. "Complementarity" means that when A and T in two strands of DNA are placed opposite each other, a bond is spontaneously formed between them. Similarly, G and C form a complementary pair. Human cells contain 46 chromosomes. The length of the human genome (all the DNA in the chromosomes) can reach two meters and consists of three billion nucleotide pairs. A gene is a unit of heredity. It is part of a DNA molecule and contains encoded information about the amino acid sequence of one protein or ribonucleic acid (RNA).

Rice. 1 . DNA.

The scientists' announcement that they had succeeded in deciphering the structure of this large molecule brought together the previously disparate results of research in biochemistry, microbiology and genetics, conducted over half a century. In recent decades, humanity has witnessed the rapid progress of genetics. This science has long become the most important asset of humanity, to which the hopes of millions of people are turned.

Gene therapy of hereditary diseases, gene transfer from one species to another (transgenosis), molecular paleogenetics are other impressive realities of science at the end of its 100-year history. Genetic engineering and biotechnology, supported by effective public propaganda, transformed the face of genetics.

In the 80s, scientists took on the task of deciphering only short DNA molecules: viral, mitochondrial or plasmid. (A plasmid is a circular DNA molecule located in the cytoplasm of bacteria and consisting of a small number of genes.) But the first steps have been taken. And then, in 1988, the most desperate researchers came up with a proposal to decipher the human genome.

After 1998, an unprecedented race began between the 1,100 scientists of the global Human Genome Project community and the private equity firm Celera Genomics to be the first to identify the entire human genome. The company, having concentrated a powerful computer base and robotics, took the lead. However, its apparent intentions to profit from patenting the composition of human DNA fragments were wisely suspended for the time being by the verdict: “What is created by Nature and God cannot be patented by man.”

The financing of the race and the participation of thousands of specialists in it are based primarily on the belief that in genetics and biology there is nothing more urgent now than the total deciphering of the nucleotide composition of DNA, that this can directly solve the main mysteries and problems of genetics and biology

Chapter 1. The subject of genetics

1.1. Modern ideas about the gene

Just as in physics the elementary units of matter are atoms, in genetics the elementary discrete units of heredity and variability are genes. The chromosome of any organism, be it a bacterium or a human, contains a long (from hundreds of thousands to billions of nucleotide pairs) continuous strand of DNA, along which many genes are located. Establishing the number of genes, their exact location on the chromosome and their detailed internal structure, including knowledge of the complete nucleotide sequence, is a task of exceptional complexity and importance. Scientists successfully solve it using a whole range of molecular, genetic, cytological, immunogenetic and other methods.

1.2. Gene structure

Transcription

Intron 2

Intron 1

Exon 3

Terminator

Promoter

Exon 2

Promoter

Promoter

Promoter

Exon 1

Promoter

According to modern concepts, the gene encoding the synthesis of a certain protein in eukaryotes consists of several essential elements. (Fig. 2) First of all, this is an extensive regulatory a zone that has a strong influence on the activity of a gene in a particular tissue of the body at a certain stage of its individual development. Next is located directly adjacent to the coding elements of the gene promoter– a DNA sequence up to 80-100 nucleotide pairs long, responsible for binding the RNA polymerase that transcribes a given gene. Following the promoter lies the structural part of the gene, which contains information about the primary structure of the corresponding protein. For most eukaryotic genes, this region is significantly shorter than the regulatory zone, but its length can be measured in thousands of nucleotide pairs.

An important feature of eukaryotic genes is their discontinuity. This means that the protein-coding region of the gene consists of two types of nucleotide sequences. Some are exons - sections of DNA that carry information about the structure of a protein and are part of the corresponding RNA and protein. Others, introns, do not encode protein structure and are not included in the mature mRNA molecule, although they are transcribed. The process of cutting out introns - “unnecessary” sections of the RNA molecule and splicing exons during the formation of mRNA is carried out by special enzymes and is called splicing(stitching, splicing). Exons are usually joined together in the same order as they appear in the DNA. However, not absolutely all eukaryotic genes are discontinuous. In other words, some genes, like bacterial ones, have a complete correspondence of the nucleotide sequence to the primary structure of the proteins they encode.

1.3. Basic concepts and methods of genetics

Representatives of any biological species reproduce creatures similar to themselves. This property of descendants to be similar to their ancestors is called heredity.

Despite the enormous influence of heredity in the formation of the phenotype of a living organism, related individuals differ to a greater or lesser extent from their parents. This property of descendants is called variability. The science of genetics studies the phenomena of heredity and variability. Thus, genetics is the science of the patterns of heredity and variability. According to modern concepts, heredity is the property of living organisms to transmit from generation to generation features of morphology, physiology, biochemistry and individual development under certain environmental conditions. Variability- a property opposite to heredity is the ability of daughter organisms to differ from their parents in morphological, physiological, biological characteristics and deviations in individual development. Heredity and variability are realized in the process of inheritance, i.e. when transmitting genetic information from parents to offspring through germ cells (during sexual reproduction) or through somatic cells (during asexual reproduction).

Genetics as a science solves the following main problems:

· studies ways of storing genetic information in different organisms (viruses, bacteria, plants, animals and humans) and its material carriers;

· analyzes ways of transmitting hereditary information from one generation of organisms to another;

· identifies mechanisms and patterns of implementation of genetic information in the process of individual development and the impact of environmental conditions on them;

· studies the patterns and mechanisms of variability and its role in adaptive reactions and in the evolutionary process;

· seeks ways to correct damaged genetic information.

To solve these problems, different research methods are used.

The method of hybridological analysis was developed by Gregor Mendel. This method allows us to identify patterns of inheritance of individual characteristics during sexual reproduction of organisms. Its essence is as follows: the analysis of inheritance is carried out according to individual independent characteristics; the transmission of these characteristics over a number of generations can be traced; An accurate quantitative account is taken of the inheritance of each alternative trait and the nature of the offspring of each hybrid separately.

The cytogenetic method allows you to study the karyotype (set of chromosomes) of body cells and identify genomic and chromosomal mutations.

The genealogical method involves the study of animal and human pedigrees and allows us to establish the type of inheritance (for example, dominant, recessive) of a particular trait, the zygosity of organisms and the likelihood of the manifestation of traits in future generations. This method is widely used in breeding and medical genetic consultations.

The twin method is based on the study of the manifestation of traits in identical and fraternal twins. It allows us to identify the role of heredity and the external environment in the formation of specific characteristics.

Biochemical research methods are based on studying the activity of enzymes and the chemical composition of cells, which are determined by heredity. Using these methods, it is possible to identify gene mutations and heterozygous carriers of recessive genes.

The population statistical method allows you to calculate the frequency of occurrence of genes and genotypes in populations.

Let us introduce the basic concepts of genetics. When studying patterns of inheritance, individuals are usually crossed that differ from each other in alternative (mutually exclusive) characters (for example, yellow and green color, smooth and wrinkled surface of peas). Genes that determine the development of alternative traits are called allelic. They are located in identical loci (locations) of homologous (paired) chromosomes. An alternative trait and the corresponding gene, manifested in first-generation hybrids, are called dominant, and those not manifested (suppressed) are called recessive. If both homologous chromosomes contain the same allelic genes (two dominant or two recessive), then such an organism is called homozygous. If different genes of one allelic pair are localized on homologous chromosomes, then such an organism is usually called heterozygous on this basis. It forms two types of gametes and, when crossed with an organism of the same genotype, produces splitting.

The set of all genes in an organism is called genotype. A genotype is a collection of genes that interact with each other and influence each other. Each gene is influenced by other genes of the genotype and itself influences them, so the same gene can manifest itself differently in different genotypes.

The totality of all the properties and characteristics of an organism is called phenotype. The phenotype develops on the basis of a specific genotype as a result of interaction with environmental conditions. Organisms that have the same genotype may differ from each other depending on the conditions of development and existence. A separate feature is called hairdryer Phenotypic characteristics include not only external characteristics (eye color, hair, nose shape, flower color, etc.), but also anatomical (stomach volume, liver structure, etc.), biochemical (glucose and urea concentration in blood serum, etc. ) and others.

Chapter 2 Heredity

2.1. Mendel's studies

An important step in understanding the laws of heredity was made by the outstanding Czech researcher Gregor Mendel. He identified the most important laws of heredity and showed that the characteristics of organisms are determined by discrete (individual) hereditary factors. The work “Experiments on Plant Hybrids” was distinguished by its depth and mathematical accuracy, but it was published in the little-known works of the Brunn Society of Naturalists and remained unknown for almost 35 years - from 1865 to 1900. It was in 1900. G. de Vries in Holland, K. Correns in Germany and E. Csermak in Austria independently rediscovered Mendel's laws and recognized his priority. The rediscovery of Mendel's laws caused the rapid development of the science of heredity and variability of organisms - genetics.

While in Vienna, Mendel became interested in the process of plant hybridization and, in particular, the different types of hybrid descendants and their statistical relationships. These problems were the subject of Mendel's scientific research, which he began in the summer of 1856.

The successes achieved by Mendel were partly due to the successful choice of the object for experiments - the garden pea (Pisum sativum). Mendel made sure that, compared to others, this species has the following advantages:

1) there are many varieties that clearly differ in a number of characteristics;

2) plants are easy to grow;

3) the reproductive organs are completely covered by the petals, so that the plant usually self-pollinates; therefore, its varieties reproduce in purity, that is, their characteristics remain unchanged from generation to generation;

4) artificial crossing of varieties is possible, and it produces quite fertile hybrids.

Of the 34 varieties of peas, Mendel selected 22 varieties that had clearly defined differences in a number of traits, and used them in his experiments with crossing. Mendel was interested in seven main characters: stem height, seed shape, seed color, fruit shape and color, flower arrangement and color. It should be noted that in choosing an experimental object, Mendel was simply lucky in some ways: the inheritance of the traits he selected did not contain a number of more complex features that were discovered later, such as incomplete dominance, dependence on more than one pair of genes, and gene linkage. This fact partly explains the fact that before Mendel, many scientists carried out similar experiments on plants, but none of them received such accurate and detailed data; in addition, they were unable to explain their results in terms of the mechanism of heredity.

2.2. Inheritance in monohybrid crosses and the law of segregation

For his first experiments, Mendel chose two varieties of plants that clearly differed in some characteristic, for example, in the arrangement of flowers: the flowers could be distributed throughout the stem (axillary) or located at the end of the stem (apical). Mendel cultivated plants that differed in one pair of alternative traits over a number of generations. In all cases, analysis of the results showed that the ratio of dominant to recessive traits in a generation was approximately 3:1.

The above example is typical of all of Mendel's experiments in which the inheritance of a single trait was studied (monohybrid crosses).

Based on these and similar results, Mendel concluded:

1. Since the original parent varieties were propagated purely (without splitting), the variety with axillary flowers should have two“axillary” factors, and in the variety with apical flowers there are two “apical” factors.

2. F1 plants contained alone factor obtained from each of the parent plants through gametes.

3. These factors in F1 do not merge, but retain their individuality.

4. The “axillary” factor dominates the “apical” factor, which is recessive. The separation of a pair of parental factors during the formation of gametes (so that only one of them ends up in each gamete) is known as Mendel's first law or law of splitting. According to this law, the characteristics of a given organism are determined by pairs of internal factors. Only one of each pair of such factors can be present in one gamete.

We now know that these factors, which determine traits such as the location of a flower, correspond to regions of the chromosome called genes.

The experiments described above, carried out by Mendel while studying the inheritance of one pair of alternative characters, serve as an example monohybrid crossing. The scheme of zygote formation in a monohybrid cross is shown in Fig. 3.

Aa

Aa

A.A.

A

Gametes

Aa

Gametes

a

A

An organism from the F1 generation, obtained from a cross between a homozygous dominant and a homozygous recessive individual, is heterozygous in its genotype, but has a dominant phenotype. In order for a recessive phenotype to occur, an organism must be homozygous for the recessive allele. In the F2 generation, individuals with a dominant phenotype can be either homozygotes or heterozygotes. If a breeder needed to find out the genotype of such an individual, then the only way to do this is through an experiment using a method called analyzing (returning) by crossing. By crossing an organism of an unknown genotype with an organism homozygous for the recessive allele of the gene being studied, this genotype can be determined by a single cross. For example, in a fruit fly Drosofila, long wings dominate the rudimentary wings. An individual with long wings can be homozygous (LL) or heterozygous (Ll). To establish its genotype, it is necessary to carry out a test cross between this fly and a fly homozygous for the recessive allele (ll). If all the descendants of this cross have long wings, then the individual with the unknown genotype is homozygous for the dominant allele. The numerical ratio of descendants of 1:1 indicates heterozygosity of an individual with an unknown genotype.

2.4. Dihybrid crossing and the law of independent distribution

Having established the ability to predict the results of crosses based on one pair of alternative traits, Mendel moved on to studying the inheritance of two pairs of such traits. Crosses between individuals that differ in two characteristics are called dihybrid.

In one of his experiments, Mendel used pea plants that differed in the shape and color of the seeds. He crossed pure-bred (homozygous) plants with smooth yellow seeds and pure-bred plants with wrinkled green seeds. All plants (the first generation of hybrids) had smooth and yellow seeds. By crossing plants. Grown from F1 seeds, he collected 556 seeds from F2 plants, among which were:

ü smooth yellow 315

ü wrinkled yellow 101

ü smooth green 108

ü wrinkled green 32

The ratio of different phenotypes was approximately 9:3:3:1 (dihybrid split). Based on these results

Mendel drew two conclusions:

1. In the F2 generation, two new combinations of characters appeared: wrinkled and yellow, smooth and green.

2. For each pair of allelomorphic characters (phenotypes determined by different alleles), a 3:1 ratio was obtained, characteristic of a monohybrid cross - among the seeds there were 423 smooth and 133 wrinkled, 416 yellow and 140 green.

These results allowed Mendel to argue that two pairs of characters, the hereditary inclinations of which were combined in the F1 generation, are separated in subsequent generations and behave independently of one another. Based on this Mendel's second law - the principle of independent distribution, according to which everyone a feature from one pair of features can be combined with any feature from another pair.

2.5. Brief summary of the essence of Mendel's hypotheses

1. Each trait of a given organism is controlled by a pair of alleles.

2. If an organism contains two different alleles for a given trait, then one of them (dominant) can manifest itself, completely suppressing the manifestation of the other trait (recessive).

3. During meiosis, each pair of alleles separates (splits) and each gamete receives one of each pair of alleles (cleavage principle).

4. When male and female gametes are formed, any allele from one pair can enter each of them along with any other from another pair (the principle of independent distribution).

5. Each allele is transmitted from generation to generation as a discrete, unchanging unit.

6. Each organism inherits one allele (for each trait) from each of its parents.

2.6. Clutch

All situations and examples discussed so far have related to the inheritance of genes located on different chromosomes. As cytologists have found out, in humans, all somatic cells contain 46 chromosomes. Since a person has thousands of different characteristics - such as blood type, eye color, the ability to secrete insulin - each chromosome must contain a large number of genes.

Genes lying on the same chromosome are called linked. All genes on any one chromosome form clutch group; they usually end up in the same gamete and are inherited together. Thus. Genes belonging to the same linkage group do not usually obey the Mendelian principle of independent distribution. Therefore, when crossed dihybridly, they do not give the expected ratio of 9:3:3:1. In such cases, a wide variety of relationships are obtained. In Drosophila, the genes that control body color and wing length are represented by the following pairs of alleles (let’s name the corresponding characteristics): gray body - black body, long wings - rudimentary (short) wings. The gray body and long wings dominate. The expected ratio of phenotypes from a cross between a homozygote with a gray body and long wings and a homozygote with a black body and rudimentary wings should be 9:3:3:1. This would indicate normal Mendelian inheritance in dihybrid crosses, due to the random distribution of genes located on different, non-homologous chromosomes. However, F2 instead produced mostly parental phenotypes in a ratio of approximately 3:1. This can be explained by assuming that the genes for body color and wing length are localized on the same chromosome, i.e. linked.

In practice, however, a 3:1 ratio is never observed, and all four phenotypes occur. This is because complete adhesion is rare. In most linkage crossing experiments, in addition to flies with parental phenotypes, flies with new combinations of traits are found. These new phenotypes are called recombinant. All this allows us to give the following definition of clutch: two or more genes are said to be linked if offspring with new gene combinations (recombinants) are less common than the parental phenotypes.

2.7. Determination of gender

A particularly clear example of a method for establishing the relationship between the phenotypic characteristics of organisms and the structure of their chromosomes is the determination of sex. In Drosophila, phenotypic differences between the two sexes are clearly related to differences in chromosomes (Fig. 4.).

Rice. 4. Chromosome sets of male and femaleD.melanogaster. They consist of four pairs of chromosomes (pairI - sex chromosomes).

When studying the chromosomes of males and females of a number of animals, some differences were discovered between them. Both male and female individuals have pairs of identical (homologous) chromosomes in all cells, but they differ in one pair of chromosomes. These are gross chromosomes (heterosomes). All other chromosomes are called autosomes. Drosophila has four pairs of chromosomes. Three pairs are identical in both sexes, but one pair, consisting of identical chromosomes in the female, is different in the male. These chromosomes are called X and Y chromosomes; The female's genotype is XX, and the male's genotype is XY. Such differences in sex chromosomes are characteristic of most animals, including humans, but in birds (including chickens) and butterflies the opposite picture is observed: females have XY chromosomes, and males have XX chromosomes. Some insects, such as Orthoptera, do not have a Y chromosome at all, so the male has the X0 genotype. In Fig. Figure 5 shows human sex chromosomes.

Rice. 5. View of human sex chromosomes in metaphase of mitosis.

During gametogenesis, typical Mendelian segregation along the sex chromosomes is observed. For example, in mammals, each egg contains one X chromosome, half of the sperm contains one Y chromosome, and the other half contains one X chromosome. The sex of the offspring depends on which sperm fertilizes the egg. In most organisms, however, the Y chromosome does not contain sex-related genes. It is even called genetically inert or genetically empty, since it contains very few genes. In Drosophila, the genes that determine male characteristics are believed to be located on autosomes, and their phenotypic effects are masked by the presence of a pair of X chromosomes; In the presence of one X chromosome, male characteristics appear. This is an example of sex-limited inheritance (as opposed to sex-linked inheritance), in which, for example, in women, genes that determine beard growth are suppressed.

Morgan and his collaborators noticed that the inheritance of eye color in Drosophila depends on the sex of the parents carrying alternative alleles. Red eye color dominates over white. When crossing a red-eyed male and a white-eyed female in F1, an equal number of red-eyed females and white-eyed males were obtained. However, when crossing a white-eyed male with a red-eyed female in F1, equal numbers of red-eyed males and females were obtained. When these flies were crossed with each other, red-eyed females, red-eyed and white-eyed males were obtained, but there was not a single white-eyed female. The fact that the frequency of manifestation of the recessive trait in males is higher than in females suggested that the recessive allele determining white-eyedness is located on the X chromosome, and the Y chromosome lacks the eye color gene. To test this hypothesis, Morgan crossed the original white-eyed male with a red-eyed F1 female. The offspring were red-eyed and white-eyed males and females. From this, Morgan rightly concluded that only the X chromosome carries the gene for eye color. There is no corresponding locus on the Y chromosome at all. This phenomenon is known as sex-linked inheritance.

2.8. Sex-linked inheritance

Genes found on sex chromosomes are called sex-linked. There is a region on the X chromosome for which there is no homologue on the Y chromosome. Therefore, in males, the traits determined by the genes of this region appear even if they are recessive. This special form of linkage helps explain the inheritance of sex-linked traits, such as color blindness. Early baldness and hemophilia in humans. Hemophilia is a sex-linked recessive trait in which the formation of factor VIII, which accelerates blood clotting, is impaired. The gene that determines the synthesis of factor VIII is located in a region of the X chromosome that does not have a homologue, and is represented by two alleles - a dominant and a recessive mutant.

One of the most well-documented examples of the inheritance of hemophilia is found in the pedigree of the descendants of Queen Victoria of England. It is believed that the hemophilia gene arose as a result of a mutation in Queen Victoria herself or in one of her parents (Fig. 5).

The following genotypes and phenotypes are possible:

Genotype

Phenotype

Normal woman

Normal female (carrier)

Normal man

The man is a hemophiliac

The woman is a hemophiliac. A rare case, possible only if the father is a hemophiliac and the mother is a hemophiliac or a carrier.

2.9. Incomplete dominance

There are cases where two or more alleles do not fully exhibit dominance or recessivity, so that in the heterozygous state, none of the alleles is dominant over the other. This phenomenon incomplete dominance, or codominance, is an exception to the rule of inheritance in monohybrid crosses described by Mendel. Fortunately, Mendel chose for his experiments traits that were not characterized by incomplete dominance; otherwise, it could greatly complicate his first research.

Incomplete dominance is observed in both plants and animals. In most cases, heterozygotes have a phenotype intermediate between the phenotypes of dominant and recessive homozygotes.

2.10. Variability

Variability is the totality of differences in one or another characteristic between organisms belonging to the same natural population or species. The striking morphological diversity of individuals within any given species attracted the attention of Darwin and Wallace during their travels. The natural, predictable nature of the inheritance of such differences served as the basis for Mendel's research. Darwin established that certain traits can develop as a result of selection, while Mendel explained the mechanism that ensures the transmission from generation to generation of traits for which selection is carried out.

Mendel described how hereditary factors determine the genotype of an organism, which during development is manifested in the structural, physiological and biochemical features of the phenotype. If the phenotypic manifestation of any trait is ultimately determined by the genes that control this trait, then the degree of development of certain traits may be influenced by the environment.

The study of phenotypic differences in any large population shows that there are two forms of variation - discrete and continuous. To study variation in a trait, such as height in humans, it is necessary to measure that trait across a large number of individuals in the population being studied. On rice. 6 Typical results obtained from such studies are presented, and they clearly demonstrate the difference between discrete and continuous variability.

Rice. 7. Histograms showing the frequency distribution in the case of intermittent (A) and continuous (B) variability.

2.11. Environmental influence

The main factor determining any phenotypic trait is the genotype. The genotype of an organism is determined at the moment of fertilization, but the degree of subsequent expression of this genetic potential depends largely on external factors affecting the organism during its development. For example, the long-stemmed pea variety used by Mendel usually reached a height of 180 cm. However, for this it needed appropriate conditions - lighting, water supply and good soil. In the absence of optimal conditions (if there are limiting factors) the tall stem gene could not fully express its effect. The effect of interaction between genotype and environmental factors was demonstrated by the Danish geneticist Johannsen. In a series of experiments on dwarf beans, he selected the heaviest and lightest seeds from each generation of self-pollinating plants and planted them to produce the next generation. Repeating these experiments over several years, he found that within a “heavy” or “light” breeding line, seeds varied little in average weight, while the average weight of seeds from different lines varied greatly. This suggests that the phenotypic manifestation of a trait is influenced by both heredity and environment. Based on these results, continuous phenotypic variation can be defined as “ the cumulative effect of varying environmental factors affecting a variable genotype.” In addition, these results show that the degree of heritability of a given trait is determined primarily by the genotype. As for the development of such purely human qualities as individuality, temperament and intelligence, then, judging by the available data, they depend on both hereditary and environmental factors, which, interacting to varying degrees in different individuals, create phenotypic differences between individuals. We do not yet have data that would firmly indicate that the influence of some of these factors always predominates, but the environment can never bring the phenotype beyond the limits determined by the genotype.

2.12. Sources of Variation

It must be clearly understood that the interaction between discrete and continuous variability and the environment makes it possible for two organisms with an identical phenotype to exist. The mechanism of DNA replication during mitosis is so close to perfection that the possibilities of genetic variability in organisms with asexual reproduction are very small. Therefore, any visible variability in such organisms is due to environmental influences. As for organisms that reproduce sexually, there is ample opportunity for genetic differences to arise. Two processes that occur during meiosis provide virtually unlimited sources of genetic variation:

1. Reciprocal exchange between chromatids of homologous chromosomes, which can occur in prophase 1 of meiosis. It creates new clutch groups, i.e. serves as an important source of genetic recombination of alleles.

2. The orientation of pairs of homologous chromosomes (bivalents) in the equatorial plane of the spindle in metaphase I of meiosis determines the direction in which each member of the pair will move in anaphase I. This operation is random. During metaphase II, pairs of chromatids are again oriented randomly, and this determines which of the two opposite poles a particular chromosome will go to during anaphase II. Random orientation and subsequent independent segregation of chromosomes make possible a large number of different chromosomal combinations in gametes; this number can be calculated.

The third source of variation in sexual reproduction is that the fusion of male and female gametes, resulting in the union of two haploid sets of chromosomes in the diploid nucleus of the zygote, occurs completely randomly (at least in theory); any male gamete has the potential to fuse with any female gamete.

These three sources of genetic variation provide the constant “shuffling” of genes that underlies genetic changes that occur all the time. The environment influences the whole range of resulting phenotypes, and those best adapted to the environment do well. This leads to changes in allele and genotype frequencies in the population. However, these sources of variation do not produce the major changes in genotype that evolutionary theory requires for the emergence of new species. Such changes occur as a result of mutations.

2.13. Mutations

A mutation is a change in the amount or structure of DNA in a given organism. The mutation results in a change in genotype that can be inherited by cells descended from the mutant cell through mitosis or meiosis. Mutation can cause changes in any characteristics in a population. Mutations that arise in germ cells are transmitted to the next generations of organisms, while mutations that arise in somatic cells are inherited only by daughter cells formed by mitosis and such mutations are called somatic.

Mutations resulting from changes in the number or macrostructure of chromosomes are known as chromosomal mutations or chromosomal aberrations(perestroika). Sometimes chromosomes change so much that it can be seen under a microscope. But the term “mutation” is used mainly to refer to a change in the DNA structure at one locus, when a so-called gene, or point, mutation occurs.

The idea of ​​mutation as the cause of the sudden appearance of a new character was first put forward in 1901 by the Dutch botanist Hugo de Vries, who studied heredity in the evening primrose Oenothera lamarckiana. Nine years later, T. Morgan began studying mutations in Drosophila, and soon, with the participation of geneticists around the world, more than 500 mutations were identified in it.

2.14. Gene mutations

Sudden spontaneous changes in phenotype, which cannot be associated with ordinary genetic phenomena or microscopic evidence of the presence of chromosomal aberrations, can only be explained by changes in the structure of individual genes. Genetic, or point(since it relates to a specific gene locus), a mutation is the result of a change in the nucleotide sequence of a DNA molecule in a certain region of the chromosome. This change in the sequence of bases in this gene is reproduced during transcription in the structure of mRNA and leads to a change in the sequence of amino acids in the polypeptide chain formed as a result of translation on ribosomes.

There are different types of gene mutations that involve the addition, deletion, or rearrangement of bases in a gene. This duplication, insertion, deletion, inversion or substitution grounds. In all cases, they lead to a change in the nucleotide sequence, and often to the formation of an altered polypeptide. For example, a deletion causes frame shift.

Gene mutations that occur in gametes or in future germ cells are transmitted to all cells of the descendants and can affect the future fate of the population. Somatic gene mutations that occur in the body are inherited only by those cells that are formed from the mutant cell through mitosis. They can have an impact on the organism in which they originated, but with death the individuals disappear from the gene pool of the population. Somatic mutations are likely to occur very frequently and go undetected, but in some cases they produce cells with increased rates of growth and division. These cells can give rise to tumors - either benign, which do not have a special effect on the entire body, or malignant, that leads to cancer diseases.

The effects of gene mutations are extremely varied. Most small gene mutations do not manifest themselves phenotypically because they are recessive, but there are a number of cases where a change in just one base in a particular gene has a profound effect on the phenotype. One example is sickle cell anemia– a disease caused in humans by a base substitution in one of the genes responsible for the synthesis of hemoglobin. The molecule of the respiratory pigment hemoglobin in an adult consists of four polypeptide chains (two a- and two b- chains), to which four heme prosthetic groups are attached. The ability of a hemoglobin molecule to carry oxygen depends on the structure of polypeptide chains. A change in the base sequence in a triplet encoding one specific amino acid out of the 146 that make up the b-chains leads to the synthesis of abnormal sickle cell hemoglobin (HbS). The amino acid sequences in normal and abnormal a-chains differ in that at one point in the abnormal chains of hemoglobin S glutamic acid replaced valine As a result of such a seemingly insignificant change, hemoglobin S crystallizes at low oxygen concentrations, and this in turn leads to the fact that in venous blood, red blood cells with such hemoglobin are deformed (from round to sickle-shaped) and quickly destroyed. The physiological effect of the mutation is the development of acute anemia and a decrease in the amount of oxygen carried by the blood. Anemia not only causes physical weakness, but can also lead to heart and kidney problems and early death in people homozygous for the mutant allele. In the heterozygous state, this allele causes a much smaller effect: red blood cells appear normal, and abnormal hemoglobin accounts for only about 40%. Heterozygotes develop only a mild form of anemia, but in areas where malaria is widespread, especially in Africa and Asia, carriers of the sickle cell allele are immune to this disease. This is explained by the fact that its causative agent - malarial plasmodium - cannot live in red blood cells containing abnormal hemoglobin.

2.15. Lethal mutations There are cases when one gene can influence several traits, including viability. Lethal mutations cause changes in development that are incompatible with life. Dominant lethal genes are difficult to study and knowledge about them is limited. In contrast, genes with recessive lethal effects have been much better studied. There are many known recessive mutations in various organisms that do not manifest themselves phenotypically. There are also many dominant mutations that have a clearly different phenotype in the heterozygous state, which in the homozygous state cause a lethal effect. The lethal phase, i.e. the time when the mutant gene is realized varies significantly: from the very first stages of embryonic development to puberty. In some cases, lethal genes may have more than one phase of lethal action. This means that a gene or its products can be actively operated and used several times during ontogeny. The lethal effect of some mutant genes always appears, while others show a significant dependence on environmental conditions. In humans and other mammals, a certain recessive gene causes the formation of internal lung adhesions, leading to death at birth. Another example is a gene that affects the formation of cartilage and causes congenital deformities leading to the death of a newborn.

The effect of a lethal gene is clearly seen in the inheritance of coat color in mice. Wild mice usually have gray fur, like an agouti; but some mice have yellow fur. When crossing yellow mice, the offspring will produce both yellow mice and agouti in a 2:1 ratio. The only possible explanation for these results is that yellow coat color is dominant in agoutis and that all yellow mice are heterozygous. The atypical Mendelian relationship is explained by the death of homozygous yellow mice before birth. Necropsies on pregnant yellow mice crossed with yellow mice revealed dead yellow pups in their uteruses. If yellow mice and agoutis were crossed, then there would be no yellow mice in the uteri of pregnant females, since such a crossing cannot produce offspring homozygous for the yellow coat gene.

Mutations that are characterized by a lethal effect in the homozygous state do not always manifest themselves phenotypically in heterozygotes. These include a complex of recessive t-mutations in mice localized in the autosome. One of the earliest mutations in mammals is the t12 mutation, which causes the death of homozygotes already at the morula stage (~20-30 cells). Heterozygous animals have normal phenotype and viability.

Lethal mutations are not only found in animals. A clear example illustrating the lethal effect of genes in plants is the phenomenon of chlorophyll mutations. In plants homozygous for the chlorophyll mutation, the synthesis of the chlorophyll molecule is impaired. Such plants develop until the supply of nutrients in the seed runs out, since they are not capable of photosynthesis.

2.16. The meaning of mutations

Chromosomal and gene mutations have a variety of effects on the body. In many cases, these mutations are lethal because they impair development; in humans, for example, about 20% of pregnancies end in natural miscarriage before 12 weeks, and in half of these cases chromosomal abnormalities can be detected. As a result of certain chromosomal mutations, certain genes may appear together, and their combined effect may lead to the appearance of some “favorable” trait. In addition, bringing some genes closer to each other makes them less likely to separate through crossing over, and in the case of favorable genes, this creates an advantage.

A gene mutation can lead to this. That there will be several alleles at a certain locus. This increases both the heterozygosity of a given population and its gene pool, and leads to increased intrapopulation variability. Gene shuffling, as a result of crossing over, independent assortment, random fertilization, and mutation, can increase continuous variation, but its evolutionary role is often transient, since the resulting changes can quickly smooth out through “averaging.” As for gene mutations, some of them increase discrete variation, and this can have a more profound effect on the population. Most gene mutations are recessive in relation to the “normal” allele, which, having successfully withstood selection over many generations, has reached genetic equilibrium with the rest of the genotype. Being recessive, mutant alleles can remain in the population for many generations until they happen to meet, i.e. be in a homozygous state and manifest itself in the phenotype. From time to time, dominant mutant alleles may arise that immediately produce a phenotypic effect.

Chapter 3. Modern opportunities and challenges of genetics and genetic engineering

3.1. Chimeras

There are broad opportunities to better understand the role of genes in cell differentiation and in the regulation of interactions between cells during development. chimeric And transgenic animals. The recent development of experimental methods has made it possible to obtain completely unusual animals that carry the genes not only of one father and one mother, but also of a larger number of ancestors.

Chimeric animals are genetic mosaics formed by combining blastomeres from embryos with different genotypes. The production of such embryos is carried out in many laboratories. The principle of obtaining chimeras comes down mainly to the isolation of two or more early embryos and their fusion. In the case where there are differences in a number of characteristics in the genotype of the embryos used to create the chimera, it is possible to trace the fate of cells of both types. With the help of chimeric mice, for example, the question of how multinucleate cells of transversely striated muscles arise during development was resolved. The study of chimeric animals has made it possible to solve many difficult questions, and in the future, thanks to the use of this method, it will be possible to solve complex problems of genetics and embryology.

3.2. Transgenic organisms

The development of genetic engineering has created a fundamentally new basis for constructing DNA sequences needed by researchers. Advances in experimental biology have made it possible to create methods for introducing such artificially created genes into the nuclei of eggs or sperm. As a result, it became possible to obtain transgenic animals those. animals that carry foreign genes in their bodies.

One of the first examples of the successful creation of transgenic animals was the production of mice in which the rat growth hormone was built into their genome. Some of these transgenic mice grew rapidly and reached sizes significantly larger than control animals.

The world's first monkey with a modified genetic code was born in America. The male, named Andy, was born after the jellyfish gene was inserted into his mother's egg. The experiment was carried out with the rhesus monkey, which is much closer in its biological characteristics to humans than any other animal that has so far been subjected to genetic modification experiments. Scientists say the technique will help them develop new treatments for diseases such as breast cancer and diabetes. However, as the BBC reports, the experiment has already drawn criticism from animal welfare groups who fear the research will lead to the suffering of many primates in laboratories.

Creation of a human-pig hybrid. The nucleus is removed from a human cell and implanted into the nucleus of a pig egg, which has previously been freed from the animal’s genetic material. The result was an embryo that lived for 32 days until scientists decided to destroy it. Research is carried out, as always, for a noble goal: finding cures for human diseases. Although attempts to clone human beings are frowned upon by many scientists and even those who created Dolly the sheep, such experiments will be difficult to stop since the principle of the cloning technique is already known to many laboratories.

Currently, there is great interest in transgenic animals. This is due to two reasons. Firstly, wide opportunities have arisen for studying the operation of a foreign gene in the genome of the host organism, depending on the location of its insertion into a particular chromosome, as well as the structure of the gene’s regulatory zone. Secondly, transgenic farm animals may be of practical interest in the future.

3.3. A little about cloning

The term " clone"comes from the Greek word" clone", which means a twig, shoot, cutting, and is primarily related to vegetative propagation. Cloning of plants by cuttings, buds or tubers in agriculture, in particular in horticulture, has been known for more than 4 thousand years. With vegetative propagation and When cloning, genes are not distributed among descendants, as in the case of sexual reproduction, but are preserved in their entirety for many generations. However, animals have an obstacle. As their cells grow, they, in the course of cellular specialization - differentiation- lose the ability to implement all the genetic information embedded in the nucleus. The possibility of cloning vertebrate embryos was first demonstrated in the early 50s in experiments on amphibians. Experiments with them have shown that serial nuclear transplantation and cell cultivation in vitro to some extent increases this ability. Already in the early 90s, the problem of cloning mammalian embryonic cells was solved. Reconstructed eggs from large domestic animals, cows or sheep are not first cultured. in vitro, A in vivo- in the tied oviduct of a sheep - the intermediate (first) recipient. They are then washed out from there and transplanted into the uterus of the final (second) recipient - a cow or sheep, respectively, where their development occurs until the baby is born.

The first cloned animal (a sheep named Dolly) appeared as a result of using a donor mammary cell nucleus adult sheep. This first successful experiment has a significant drawback - a very low yield of live individuals (0.36%). However, it proves the possibility of full cloning, (or obtaining a copy of an adult). All that remains is to resolve technical and ethical issues.

But let's return to human cloning. There is also a rather elegant way to get around ethical problems. Let us remember that, oddly enough, pigs are closest to humans in the structure of internal organs.

In March 2000, PPL Therapeutics announced that five cloned piglets were born at their research center. Cloning a pig is a more complex operation than cloning sheep or cows, since several healthy fetuses are needed to support one pregnancy. Pig organs are the most similar in size to humans. Pigs breed easily and are known for being unpretentious. But the biggest problem remains the rejection of an animal organ, which the human body does not accept as its own. It is in this direction that further research by scientists will develop. Scientists see one possible way to solve this problem is to genetically “camouflage” the animal’s organs so that the human body cannot recognize them as foreign. Another topic for research is the attempt to genetically “humanize” pig organs in order to significantly reduce the risk of rejection. To do this, it is proposed to introduce human genes into the chromosomes of cloned pigs.

Other institutes are also engaged in the same task, but without the use of cloning. For example, the Cambridge-based company Imutran was able to obtain an entire herd of pigs whose genetic makeup no longer contained one of the key characteristics responsible for the rejection of foreign tissue. Once a male and female pair is produced, they will be ready to produce "genetically pure offspring" with organs that can be used for transplantation.

Another step towards immortality is the artificial change of DNA. In June 2000, what happened for so long and what some were so afraid of happened. There was a message that scientists from the Scottish company PPL Therapeutics, already famous for its sheep Dolly, managed to obtain successful clones of sheep with altered DNA. Scottish scientists were able to carry out cloning, in which the genetic material of the clone was “tweaked” for the better. There is also an already legalized way to circumvent the ban on human cloning, which is called “therapeutic” cloning of human beings. We are talking about creating early embryos - a kind of bank of donor tissue for specific individuals.

For this purpose they are used stem cells(simplified - cells of early human embryos). The growth potential of stem cells is simply fantastic - just remember that the trillion-cell organism of a newborn human is formed from a single cell in just 9 months! But even more impressive is the potential for differentiation - the same stem cell can transform into any(!) human cell, be it a brain neuron, a liver cell or a cardiac myocyte. “Adult” cells are unable to undergo such a transformation.

But one unique property of these cells truly turns them into the hope of humanity - they are rejected much less easily than transplanted whole organs consisting of already differentiated cells. This means that, in principle, it is possible to grow precursors of a wide variety of cells (heart, nerve, liver, immune, etc.) in laboratory conditions, and then transplant them into seriously ill people instead of donor organs.

And in January 2001, information appeared about a discovery that could make cloning simply unnecessary. It was possible to reverse the biological clock inside a human cell, causing it to return to the state in which it was at the time of formation in the embryo.

3.4. Treatment and prevention of some hereditary human diseases

The increased interest of medical genetics in hereditary diseases is explained by the fact that in many cases, knowledge of the biochemical mechanisms of development makes it possible to alleviate the suffering of the patient. The patient is injected with enzymes that are not synthesized in the body. For example, diabetes mellitus is characterized by an increase in the concentration of sugar in the blood due to insufficient (or complete absence) production of the hormone insulin by the pancreas in the body. This disease is caused by a recessive gene. Back in the 19th century, this disease almost inevitably led to the death of the patient. Extracting insulin from the pancreas of some pets has saved the lives of many people. Modern methods of genetic engineering have made it possible to produce insulin of much higher quality, absolutely identical to human insulin on a scale sufficient to provide every patient with insulin and at much lower costs.

Nowadays, hundreds of diseases are known in which the mechanisms of biochemical disorders have been studied in sufficient detail. In some cases, modern microanalysis methods make it possible to detect such biochemical disorders even in individual cells, and this, in turn, makes it possible to diagnose the presence of such diseases in an unborn child based on individual cells in the amniotic fluid.

3.5. Medical genetic counseling

Knowledge of human genetics allows us to predict the likelihood of having children suffering from hereditary diseases, when one or both spouses are sick or both parents are healthy, but the hereditary disease occurred in the ancestors of the spouses. In some cases, it is possible to predict the probability of having a second healthy child if the first one was affected by a hereditary disease.

As the biological and especially genetic education of the general population increases, married couples who do not yet have children are increasingly turning to geneticists with the question of the risk of having a child affected by a hereditary anomaly.

Medical genetic consultations are now open in many regions and regional centers of our country. The widespread use of medical and genetic consultations will play an important role in reducing the incidence of hereditary diseases and will save many families from the misfortune of having unhealthy children.

Currently, the amniocentesis method is widely used in many countries, allowing the analysis of embryonic cells from amniotic fluid. Thanks to this method, a woman at an early stage of pregnancy can obtain important information about possible chromosomal or gene mutations of the fetus and avoid the birth of a sick child.

Conclusion

So, the work outlined the key concepts of genetics, its methods and achievements in recent years. Genetics is a very young science, but the pace of its development is so high that at the moment it occupies the most important place in the system of modern sciences, and, perhaps, the most important achievements of the last decade of the past century are associated with genetics. Now, at the beginning of the 21st century, prospects are opening up before humanity that captivate the imagination. Will scientists be able to realize the gigantic potential inherent in genetics in the near future? Will humanity receive the long-awaited deliverance from hereditary diseases, will man be able to prolong his too short life and gain immortality? At present we have every reason to hope for this.

According to geneticists, by the end of the first decade of the 21st century, genetic vaccines will replace conventional vaccinations, and doctors will have the opportunity to forever put an end to such incurable diseases as cancer, Alzheimer's disease, diabetes, and asthma. This direction already has its own name - gene therapy. She was born just five years ago. But it may soon lose its relevance thanks to gene diagnostics. According to some forecasts, around 2020, exceptionally healthy children will be born: already at the embryonic stage of fetal development, geneticists will be able to correct hereditary problems. Scientists predict that in 2050 there will be attempts to improve the human species. By this time, they will learn to design people of a certain specialization: mathematicians, physicists, artists, poets, and perhaps geniuses.

And closer to the end of the century, man’s dream will finally come true: the aging process, undoubtedly, can be controlled, and then immortality will not be far away.

Literature.

N. Grinn, Biology, Moscow, MIR, 1993.

F. Kibernstern, Genes and genetics. Moscow, “Paragraph”, 1995.

R.G. Hare et al., Biology for university applicants. MN: Higher School, 1999

M.M. Tikhomirova, Genetic analysis: textbook. – L.: Leningrad University Publishing House, 1990.

General biology. A textbook for grades 10-11 in schools with in-depth study of biology. Edited by Professor A.O. Ruchinsky. Moscow, “Enlightenment” 1993.

Nature. 1999. pp. 309-312 (Great Britain).

Heredity and genes, Science and Life, March 1999

Introduction………………………………………………………………………3

Chapter 1. Subject of genetics……………………………………………....4

1.1 What genetics studies……………………………………………....4

1.2. Modern ideas about the gene…………………………….5

1.2. Gene structure……………………………………………………...6

1.4. Problems and methods of genetics research…………………9

1.5. The main stages of the development of genetics…………………………..11

1.6 Genetics and humans…………………………………………….18

Chapter 2. The role of reproduction in the development of living things……………. 23

2.1. Features of cyclic reproduction……………23

Conclusion………………………………………………………...27

Bibliographic list of used literature…………….…29

Introduction

For my work on the subject “Concepts of modern natural science,” I chose the topic “Main problems of genetics and the role of reproduction in the development of living things,” because genetics is one of the main, most fascinating and at the same time complex disciplines of modern natural science.

Genetics, which turned the biology of the 20th century into an exact scientific discipline, continuously amazes the imagination of “broad layers” of the scientific and pseudo-scientific community with new directions and more and more new discoveries and achievements. For thousands of years, people have used genetic methods to improve the beneficial properties of cultivated plants and breed highly productive breeds of domestic animals, without having any understanding of the mechanisms underlying these methods.

Only at the beginning of the  century did scientists begin to fully realize the importance of the laws of heredity and its mechanisms. Although the success of microscopy made it possible to establish that hereditary characteristics are transmitted from generation to generation through sperm and eggs, it remained unclear how the smallest particles of protoplasm could carry the “makings” of that huge variety of characteristics that make up each individual organism.

Chapter 1. Subject of genetics

1.1 What genetics studies.

Genetics is the science of heredity and variability of organisms. Genetics is a discipline that studies the mechanisms and patterns of heredity and variability of organisms, methods of controlling these processes. It is intended to reveal the laws of reproduction of living things through generations, the emergence of new properties in organisms, the laws of individual development of an individual and the material basis of historical transformations of organisms in the process of evolution.

Depending on the object of study, plant genetics, animal genetics, microbial genetics, human genetics, etc. are distinguished, and depending on the methods used in other disciplines, biochemical genetics, molecular genetics, environmental genetics, etc.

Genetics makes a huge contribution to the development of the theory of evolution (evolutionary genetics, population genetics). Ideas and methods of genetics find application in all areas of human activity related to living organisms. They are important for solving problems in medicine, agriculture, and the microbiological industry. The latest advances in genetics are associated with the development of genetic engineering.

In modern society, genetic issues are widely discussed in different audiences and from different points of view, including ethical ones, obviously for two reasons.

The need to understand the ethical aspects of using new technologies has always arisen.

The difference between the modern period is that the speed of implementation of an idea or scientific development has increased sharply as a result.

1.2. Modern ideas about the gene.

The role of genes in the development of the body is enormous. Genes characterize all the characteristics of the future organism, such as eye and skin color, size, weight and much more. Genes are carriers of hereditary information on the basis of which an organism develops.

Just as in physics the elementary units of matter are atoms, in genetics the elementary discrete units of heredity and variability are genes. The chromosome of any organism, be it a bacterium or a human, contains a long (from hundreds of thousands to billions of nucleotide pairs) continuous strand of DNA, along which many genes are located. Establishing the number of genes, their exact location on the chromosome and their detailed internal structure, including knowledge of the complete nucleotide sequence, is a task of exceptional complexity and importance. Scientists successfully solve it using a whole range of molecular, genetic, cytological, immunogenetic and other methods.

1.2. Gene structure.

Coding chain

Regulatory zone

Promoter

Exon 1

Promoter

Promoter

Promoter

Intron 1

Exon 2

Promoter

Exon 3

Intron2

Terminator

mRNA

Transcription

Splicing

Mature mRNA

According to modern concepts, the gene encoding the synthesis of a certain protein in eukaryotes consists of several essential elements. (Fig) First of all, this is an extensive regulatory a zone that has a strong influence on the activity of a gene in a particular tissue of the body at a certain stage of its individual development. Next is the promoter, directly adjacent to the coding elements of the gene -

a DNA sequence up to 80-100 nucleotide pairs long, responsible for binding the RNA polymerase that transcribes a given gene. Following the promoter lies the structural part of the gene, which contains information about the primary structure of the corresponding protein. For most eukaryotic genes, this region is significantly shorter than the regulatory zone, but its length can be measured in thousands of nucleotide pairs.

An important feature of eukaryotic genes is their discontinuity. This means that the protein-coding region of the gene consists of two types of nucleotide sequences. Some are exons - sections of DNA that carry information about the structure of a protein and are part of the corresponding RNA and protein. Others, introns, do not encode protein structure and are not included in the mature mRNA molecule, although they are transcribed. The process of cutting out introns - “unnecessary” sections of the RNA molecule and splicing exons during the formation of mRNA is carried out by special enzymes and is called splicing(stitching, splicing). Exons are usually joined together in the same order as they appear in the DNA. However, not absolutely all eukaryotic genes are discontinuous. In other words, some genes, like bacterial ones, have a complete correspondence of the nucleotide sequence to the primary structure of the proteins they encode.

1.3. Basic concepts and methods of genetics.

Let us introduce the basic concepts of genetics. When studying patterns of inheritance, individuals are usually crossed that differ from each other in alternative (mutually exclusive) characters (for example, yellow and green color, smooth and wrinkled surface of peas). Genes that determine the development of alternative traits are called allelic. They are located in identical loci (locations) of homologous (paired) chromosomes. An alternative trait and the corresponding gene, manifested in first-generation hybrids, are called dominant, and those not manifested (suppressed) are called recessive. If both homologous chromosomes contain the same allelic genes (two dominant or two recessive), then such an organism is called homozygous. If different genes of one allelic pair are localized on homologous chromosomes, then such an organism is usually called heterozygous on this basis. It forms two types of gametes and, when crossed with an organism of the same genotype, produces splitting.

The set of all genes in an organism is called genotype. A genotype is a collection of genes that interact with each other and influence each other. Each gene is influenced by other genes of the genotype and itself influences them, so the same gene can manifest itself differently in different genotypes.

The totality of all the properties and characteristics of an organism is called phenotype. The phenotype develops on the basis of a specific genotype as a result of interaction with environmental conditions. Organisms that have the same genotype may differ from each other depending on conditions.

Representatives of any biological species reproduce creatures similar to themselves. This property of descendants to be similar to their ancestors is called heredity.

Features of the transmission of hereditary information are determined by intracellular processes: mitosis and meiosis. Mitosis is the process of distributing chromosomes to daughter cells during cell division. As a result of mitosis, each chromosome of the parent cell is duplicated and identical copies disperse to the daughter cells; in this case, hereditary information is completely transmitted from one cell to two daughter cells. This is how cell division occurs in ontogenesis, i.e. process of individual development. Meiosis is a specific form of cell division that occurs only during the formation of sex cells, or gametes (sperm and eggs). Unlike mitosis, the number of chromosomes during meiosis is halved; each daughter cell receives only one of the two homologous chromosomes of each pair, so that in half of the daughter cells there is one homologue, in the other half there is another; in this case, chromosomes are distributed in gametes independently of each other. (The genes of mitochondria and chloroplasts do not follow the law of equal distribution during division.) When two haploid gametes merge (fertilization), the number of chromosomes is restored again - a diploid zygote is formed, which received a single set of chromosomes from each parent.

Despite the enormous influence of heredity in the formation of the phenotype of a living organism, related individuals differ to a greater or lesser extent from their parents. This property of descendants is called variability. The science of genetics studies the phenomena of heredity and variability. Thus, genetics is the science of the patterns of heredity and variability. According to modern concepts, heredity is the property of living organisms to transmit from generation to generation features of morphology, physiology, biochemistry and individual development under certain environmental conditions. Variability- a property opposite to heredity is the ability of daughter organisms to differ from their parents in morphological, physiological, biological characteristics and deviations in individual development.

The study of phenotypic differences in any large population shows that there are two forms of variation - discrete and continuous. To study variation in a trait, such as height in humans, it is necessary to measure that trait across a large number of individuals in the population being studied.

Heredity and variability are realized in the process of inheritance, i.e. when transmitting genetic information from parents to offspring through germ cells (in sexual reproduction) or through somatic cells (in asexual reproduction) Today, genetics is a single comprehensive science that uses both biological and physicochemical methods to solve a wide range of major biological problems.

1.4. Problems and methods of genetics research.

The global fundamental issues of modern genetics include the following problems:

1. Variability of the hereditary apparatus of organisms (mutagenesis, recombinogenesis and directed variability), which plays a vital role in selection, medicine and the theory of evolution.

2. Environmental problems associated with the genetic consequences of chemical and radiation pollution of the environment surrounding people and other organisms.

3. Growth and reproduction of cells and their regulation, formation of a differentiated organism from one cell and control of development processes; cancer problem.

4. The problem of protecting the body, immunity, tissue compatibility during tissue and organ transplantation.

5. The problem of aging and longevity.

6. The emergence of new viruses and the fight against them.

7. Particular genetics of different species of plants, animals and microorganisms, allowing to identify and isolate new genes for use in biotechnology and breeding.

8. The problem of productivity and quality of agricultural plants and animals, their resistance to adverse environmental conditions, infections and pests.

To solve these problems, different research methods are used.

Method hybridological analysis was developed by Gregor Mendel. This method allows us to identify patterns of inheritance of individual characteristics during sexual reproduction of organisms. Its essence is as follows: the analysis of inheritance is carried out according to individual independent characteristics; the transmission of these characteristics over a number of generations can be traced; An accurate quantitative account is taken of the inheritance of each alternative trait and the nature of the offspring of each hybrid separately.

Cytogenetic method allows you to study the karyotype (set of chromosomes) of body cells and identify genomic and chromosomal mutations.

Genealogical method involves the study of the pedigrees of animals and humans and allows us to establish the type of inheritance (for example, dominant, recessive) of a particular trait, the zygosity of organisms and the likelihood of the manifestation of traits in future generations. This method is widely used in breeding and medical genetic consultations.

Twin method is based on the study of the manifestation of traits in identical and fraternal twins. It allows us to identify the role of heredity and the external environment in the formation of specific characteristics.

Biochemical methods Research is based on the study of enzyme activity and the chemical composition of cells, which are determined by heredity. Using these methods, it is possible to identify gene mutations and heterozygous carriers of recessive genes.

Population statistical method allows you to calculate the frequency of occurrence of genes and genotypes in populations.

development and existence. A separate feature is called hairdryer. Phenotypic characteristics include not only external characteristics (eye color, hair, nose shape, flower color, etc.), but also anatomical (stomach volume, liver structure, etc.), biochemical (glucose and urea concentration in blood serum, etc. ) and others.

1.5. The main stages of development of genetics.

The origins of genetics, like any science, should be sought in practice. Genetics arose in connection with the breeding of domestic animals and the cultivation of plants, as well as with the development of medicine. Since man began to use the crossing of animals and plants, he was faced with the fact that the properties and characteristics of the offspring depend on the properties of the parent individuals chosen for crossing.

The development of the science of heredity and variability was especially strongly promoted by Charles Darwin's doctrine of the origin of species, which introduced into biology the historical method of studying the evolution of organisms. Darwin himself put a lot of effort into studying heredity and variability. He collected a huge amount of facts and made a number of correct conclusions based on them, but he was unable to establish the laws of heredity. His contemporaries, the so-called hybridizers, who crossed various forms and looked for the degree of similarity and difference between parents and descendants, were also unable to establish general patterns of inheritance.

First The real scientific step forward in the study of heredity was made by the Austrian monk Gregor Mendel (1822-1884), who in 1866 published an article that laid the foundations of modern genetics. Mendel showed that hereditary inclinations do not mix, but are transmitted from parents to descendants in the form of discrete (separate) units. These units, present in pairs in individuals, remain discrete and are transmitted to subsequent generations in male and female gametes, each of which contains one unit from each pair.

Brief summary of the essence of Mendel's hypotheses

1. Each trait of a given organism is controlled by a pair of alleles.

2. If an organism contains two different alleles for a given trait, then one of them (dominant) can manifest itself, completely suppressing the manifestation of the other trait (recessive).

3. During meiosis, each pair of alleles is separated (split) and each gamete receives one of each pair of alleles (cleavage principle).

4. During the formation of male and female gametes, any allele from one pair can enter each of them along with any other from another pair (the principle of independent distribution).

5.Each allele is passed on from generation to generation as a discrete, unchanging unit.

6.Each organism inherits one allele (for each trait) from each parent.

For the theory of evolution, these principles were of cardinal importance. They revealed one of the most important sources of variability, namely the mechanism for maintaining the fitness of the characteristics of a species over a number of generations. If the adaptive characteristics of organisms that arose under the control of selection were absorbed and disappeared during crossing, then the progress of the species would be impossible.

All subsequent development of genetics was associated with the study and expansion of these principles and their application to the theory of evolution and selection.

On the second stage August Weissmann (1834-1914) showed that germ cells are isolated from the rest of the body and therefore are not subject to influences acting on somatic tissues.

Despite Weismann's convincing experiments, which were easy to verify, Lysenko's supporters, who were victorious in Soviet biology, denied genetics for a long time, calling it Weismannism-Morganism. In this case, ideology defeated science, and many scientists, such as N.I. Vavilov, were repressed.

On the third stage Hugo de Vries (1848-1935) discovered the existence of heritable mutations that form the basis of discrete variability. He suggested that new species arose due to mutations.

Mutations are partial changes in the structure of a gene. Its final effect is a change in the properties of proteins encoded by mutant genes. The trait that appears as a result of mutation does not disappear, but accumulates. Mutations are caused by radiation, chemical compounds, temperature changes and can be simply random.

On the fourth stage, Thomas Maughan (1866-1945) created the chromosome theory of heredity, according to which each biological species has a strictly defined number of chromosomes.

On the fifth stage G. Meller in 1927 established that the genotype can change under the influence of X-rays. This is where induced mutations originate, and what was later called genetic engineering with its enormous possibilities and dangers of interfering with the genetic mechanism.

On the sixth stage J. Beadle and E. Tatum in 1941 identified the genetic basis of biosynthesis.

On the seventh stage, James Watson and Francis Crick proposed a model of the molecular structure of DNA and the mechanism of its replication. They found that each DNA molecule is composed of two polydeoxyribonucleic chains, spirally twisted around a common axis.

In the period from the 40s to the present time, a number of discoveries (mainly on microorganisms) of completely new genetic phenomena have been made, revealing the possibilities of analyzing gene structure at the molecular level. In recent years, with the introduction of new research methods into genetics, borrowed from microbiology, we have come to the solution to how genes control the sequence of amino acids in a protein molecule.

First of all, it should be said that it has now been fully proven that the carriers of heredity are chromosomes, which consist of a bundle of DNA molecules.

Quite simple experiments were carried out: pure DNA was isolated from killed bacteria of one strain with a special external characteristic and transferred to living bacteria of another strain, after which the reproducing bacteria of the latter acquired the characteristic of the first strain. Numerous similar experiments show that DNA is the carrier of heredity.

Currently, approaches have been found to solving the problem of organizing the hereditary code and experimentally deciphering it. Genetics, together with biochemistry and biophysics, has come close to elucidating the process of protein synthesis in a cell and the artificial synthesis of protein molecules. This begins a completely new stage in the development of not only genetics, but all biology as a whole.

The development of genetics to this day is a continuously expanding background of research into the functional, morphological and biochemical discreteness of chromosomes. A lot has already been done in this area, a lot has already been done, and every day the cutting edge of science is approaching the goal - unraveling the nature of the gene. To date, a number of phenomena have been established that characterize the nature of the gene. Firstly, a gene on a chromosome has the property of self-reproduction (autoreproduction); secondly, it is capable of mutational change; thirdly, it is associated with a certain chemical structure of deoxyribonucleic acid - DNA; fourthly, it controls the synthesis of amino acids and their sequences in protein molecules. In connection with recent research, a new idea of ​​the gene as a functional system is being formed, and the effect of the gene on determining traits is considered in an integral system of genes - the genotype.

The emerging prospects for the synthesis of living matter attract great attention from geneticists, biochemists, physicists and other specialists.

Over the past decades, there has been a qualitative change in genetics as a science: a new research methodology has emerged - genetic engineering, which has revolutionized genetics and led to the rapid development of molecular genetics and genetic engineering biotechnology.

The modern development of general and specific genetics, molecular genetics and genetic engineering occurs with mutual enrichment of ideas and methods and is compiled through purely genetic analysis, i.e. obtaining mutations and carrying out certain crosses. It was possible to reveal many fundamental laws of life, i.e. Already in the early stages of its development, genetics became an exact experimental science.

Without highly developed general and molecular genetics, there can be no effective progress in virtually any area of ​​modern biology, selection, or protection of people's hereditary health.

Genetics and genetic engineering are no less important in the development of the national economy.

Modern selection uses methods of induced mutations and recombinations, heterosis, polyploidy, immunogenetics, cell engineering, distant hybridization, protein and DNA markers and others. Their implementation in breeding centers is extremely fruitful.

Currently, industrial microbiological synthesis of a number of products necessary for medicine, agriculture and industry is carried out using genetic engineering. The synthesis of other valuable products is carried out in cell cultures.

The development of microbial genetics largely determines the efficiency of the microbiological industry.

Now a new stage in the development of genetic engineering is being outlined - the transition to the use of plants and animals with genes responsible for the synthesis of the corresponding products transplanted into them as sources of valuable products, i.e. creation and use of transgenic plants and animals. By creating transgenic organisms, the problems of obtaining new plant varieties and animal breeds with increased productivity, as well as resistance to infectious diseases and unfavorable environmental conditions will be solved.

The development of genetic engineering has created a fundamentally new basis for constructing DNA sequences needed by researchers. Advances in experimental biology have made it possible to create methods for introducing such artificially created genes into the nuclei of eggs or sperm. As a result, it became possible to obtain transgenic animals, those. animals that carry foreign genes in their bodies.

One of the first examples of the successful creation of transgenic animals was the production of mice in which the rat growth hormone was built into their genome. Some of these transgenic mice grew rapidly and reached sizes significantly larger than control animals.

The world's first monkey with a modified genetic code was born in America. The male, named Andy, was born after the jellyfish gene was inserted into his mother's egg. The experiment was carried out with the rhesus monkey, which is much closer in its biological characteristics to humans than any other animal that has so far been subjected to genetic modification experiments. Scientists say the technique will help them develop new treatments for diseases such as breast cancer and diabetes. However, as the BBC reports, the experiment has already drawn criticism from animal welfare groups who fear the research will lead to the suffering of many primates in laboratories.

Creation of a human-pig hybrid. The nucleus is removed from a human cell and implanted into the nucleus of a pig egg, which has previously been freed from the animal’s genetic material. The result was an embryo that lived for 32 days until scientists decided to destroy it. Research is carried out, as always, for a noble goal: finding cures for human diseases. Although attempts to clone human beings are frowned upon by many scientists and even those who created Dolly the sheep, such experiments will be difficult to stop since the principle of the cloning technique is already known to many laboratories.

Currently, there is great interest in transgenic animals. This is due to two reasons. Firstly, wide opportunities have arisen for studying the operation of a foreign gene in the genome of the host organism, depending on the location of its insertion into a particular chromosome, as well as the structure of the gene’s regulatory zone. Secondly, transgenic farm animals may be of practical interest in the future.

Of great importance for medicine is the development of methods for prenatal diagnosis of genetic defects and those structural features of the human genome that contribute to the development of serious diseases: cancer, cardiovascular, mental and others.

The task has been set to create national and global genetic monitoring, i.e. tracking the genetic load and gene dynamics in people's heritage. This will be of great importance for assessing the influence of environmental mutagens and monitoring demographic processes.

The development of methods for correcting genetic defects through gene transplantation (hemotherapy) began and will develop in the 90s.

Advances in the field of studying the functioning of various genes will make it possible in the 90s to approach the development of rational methods of treating tumor, cardiovascular, and a number of viral and other dangerous diseases of humans and animals.

1.6 Genetics and humans.

In human genetics, the direct connection of scientific research with ethical issues is clearly visible, as well as the dependence of scientific research on the ethical meaning of their final results. Genetics has advanced so much that man is on the threshold of such power that allows him to determine his biological destiny. That is why the use of all the potential possibilities of medical genetics is possible only with strict adherence to ethical standards.

Human genetics, rapidly developing in recent decades, has provided answers to many of the questions that have long interested people: what determines the sex of a child? Why do children look like their parents? Which signs and diseases are inherited and which are not, why are people so different from each other, why are closely related marriages harmful?

Interest in human genetics is due to several reasons. Firstly, this is a person’s natural desire to know himself. Secondly, after many infectious diseases were defeated - plague, cholera, smallpox, etc. - the relative proportion of hereditary diseases increased. Thirdly, once the nature of mutations and their significance in heredity were understood, it became clear that mutations can be caused by environmental factors that had not previously been given due attention. An intensive study of the effects of radiation and chemicals on heredity began. Every year, more and more chemical compounds are used in everyday life, agriculture, food, cosmetics, pharmacological industries and other areas of activity, among which many mutagens are used.

In this regard, the following main problems of genetics can be identified.

Hereditary diseases and their causes. Hereditary diseases can be caused by disturbances in individual genes, chromosomes or sets of chromosomes. For the first time, a connection between an abnormal number of chromosomes and sharp deviations from normal development was discovered in the case of Down syndrome.

In addition to chromosomal disorders, hereditary diseases can be caused by changes in genetic information directly in genes.

There are no effective treatments for hereditary diseases yet. However, there are treatment methods that alleviate the condition of patients and improve their well-being. They are based mainly on compensation for metabolic defects caused by disturbances in the genome.

Medical genetic laboratories. Knowledge of human genetics allows us to determine the likelihood of having children suffering from hereditary diseases in cases where one or both spouses are sick or both parents are healthy, but hereditary diseases occurred in their ancestors. In some cases, it is possible to predict the birth of a healthy second child if the first one was sick. Such forecasting is carried out in medical genetic laboratories. The widespread use of medical genetic consultations will save many families from the misfortune of having sick children.

Are abilities inherited? Scientists believe that every person has a grain of talent. Talent is developed through hard work. Genetically, a person is richer in his capabilities, but does not fully realize them in his life.
There are still no methods for identifying a person’s true abilities in the process of his childhood and youth education, and therefore the appropriate conditions for their development are often not provided.

Does natural selection operate in human society? The history of mankind is a change in the genetic structure of populations of the species Homo sapiens under the influence of biological and social factors. Wars and epidemics changed the gene pool of humanity. Natural selection has not weakened over the past 2 thousand years, but only changed: social selection has been layered on top of it.

Genetic Engineering uses the most important discoveries of molecular genetics to develop new research methods, obtain new genetic data, as well as in practical activities, in particular in medicine.

Previously, vaccines were made only from killed or weakened bacteria or viruses that could induce immunity in humans due to the formation of specific antibody proteins. Such vaccines lead to the development of lasting immunity, but they also have disadvantages.

It is safer to vaccinate with pure proteins of the shells of viruses - they cannot multiply, because they do not have nucleic acids, but cause the production of antibodies. They can be obtained using genetic engineering methods. Such a vaccine has already been created against infectious hepatitis (Botkin's disease), a dangerous and difficult-to-treat disease. Work is underway to create pure vaccines against influenza, anthrax and other diseases.

Gender correction. Gender correction operations in our country began to be performed about 30 years ago strictly for medical reasons.

Organ transplantation. Organ transplantation from donors is a very complex operation, followed by an equally difficult period of graft engraftment. Very often the graft is rejected and the patient dies. Scientists hope that these problems can be solved through cloning.

Cloning- a method of genetic engineering in which descendants are obtained from the somatic cell of an ancestor and therefore have exactly the same genome.

Cloning animals allows us to solve many problems in medicine and molecular biology, but at the same time it gives rise to many social problems.

Scientists see the prospect of reproducing individual tissues or organs of seriously ill people for subsequent transplantation - in this case there will be no problems with transplant rejection. Cloning can also be used to obtain new drugs, especially those obtained from tissues and organs of animals or humans.

However, despite the attractive prospects, the ethical side of cloning raises concerns.

Deformities. The development of a new living being occurs in accordance with the genetic code recorded in DNA, which is contained in the nucleus of every cell in the body. Sometimes, under the influence of environmental factors - radioactive, ultraviolet rays, chemicals - the genetic code is disrupted, mutations and deviations from the norm occur.

Genetics and criminology. In judicial practice, there are cases of establishing kinship when children were confused in the maternity hospital. Sometimes this concerned children who grew up in other people's families for more than one year. To establish kinship, biological examination methods are used, which is carried out when the child turns 1 year old and the blood system has stabilized. A new method has been developed - gene fingerprinting, which allows analysis at the chromosomal level. In this case, the age of the child does not matter, and the relationship is established with a 100% guarantee.

Chapter 2. The role of reproduction in the development of living things.

2.1. Features of cyclic reproduction.

All stages in the life of any living creature are important, including for humans. They all boil down to the cyclical reproduction of the original living organism. And this process of cyclical reproduction began about 4 billion years ago.

Let's consider its features. It is known from biochemistry that many reactions of organic molecules are reversible. For example, protein molecules are synthesized from amino acids, which can be broken down into amino acids. That is, under the influence of any influences, both synthesis reactions and splitting reactions occur. In living nature, any organism goes through cyclic stages of splitting the original organism and reproducing from the separated part a new copy of the original organism, which then again produces an embryo for reproduction. It is for this reason that interactions in living nature last continuously for billions of years. The property of reproducing a copy from the split parts of the original organism is determined by the fact that a complex of molecules is transferred to the new organism, which completely controls the process of recreating the copy.

The process began with the self-reproduction of molecular complexes. And this path is quite well recorded in every living cell. Scientists have long noticed that in the process of embryogenesis the stages of the evolution of life are repeated. But then you should also pay attention to the fact that in the very depths of the cell, in its nucleus, there are DNA molecules. This is the best evidence that life on Earth began with the reproduction of complexes of molecules that had the property of first splitting the double helix of DNA, and then provided the process of recreating the double helix. This is the process of cyclical recreation of a living object with the help of molecules that were transferred at the moment of splitting and which completely controlled the synthesis of a copy of the original object. Therefore, the definition of life will look like this. Life is a type of interaction of matter, the main difference of which from known types of interactions is the storage, accumulation and copying of objects that bring certainty to these interactions and transfer them from random to regular, while cyclic reproduction of a living object occurs.

Any living organism has a genetic set of molecules that completely determines the process of recreating a copy of the original object. That is, in the presence of the necessary nutrients, with a probability of one, as a result of the interaction of a complex of molecules, a copy of a living organism will be recreated. But the receipt of nutrients is not guaranteed; harmful external influences and disruption of interactions within the cell also occur. Therefore, the total probability of recreating a copy is always slightly less than one. So, of two organisms or living objects, the organism that has the greater total probability of carrying out all the necessary interactions will be copied more efficiently. This is the law of evolution of living nature. In other words, it can be formulated this way: the more interactions necessary for copying an object are controlled by the object itself, the greater the likelihood of its cyclic reproduction.

It is obvious that if the total probability of all interactions increases, then this object evolves; if it decreases, then it involutions; if it does not change, then the object is in a stable state.

The most important function of life is the function of self-production. In other words, life activity is the process of satisfying the need for a person to reproduce his living being within the framework of the system in which he is included as an element, i.e. under environmental conditions. Taking as the initial thesis the premise that life activity has the most important need for the reproduction of its subject, as the owner of the human body, it should be noted that reproduction is carried out in two ways: firstly, in the process of consuming matter and energy from the environment, and secondly, in the process of biological reproduction, that is, the birth of offspring. The first type of realization of the need in the “external environment-organism” link can be expressed as the reproduction of “living things from non-living things”. Man exists on earth thanks to the constant consumption of necessary substances and energy from the environment.

IN AND. Vernadsky, in his famous work “Biosphere,” presented the process of life on Earth as a constant cycle of matter and energy, in which humans must be included, along with other creatures. Atoms and molecules of physical substances that make up the Earth's biosphere have been included in and out of its circulation millions of times during the existence of life. The human body is not identical to the substance and energy consumed from the external environment; it is the object of its life activity transformed in a certain way. As a result of the realization of the needs for substances, energy, and information, another object of nature arises from one object, possessing properties and functions that are not at all inherent in the original object. This reveals a special, necessarily inherent type of human activity. Such activity can be defined as a need aimed at material and energy reproduction. The content of the realization of this need is the extraction of means of life from the environment. Extraction in the broad sense includes both extraction itself and production.

This type of reproduction is not the only one necessary for the existence of life. V.I. Vernadsky wrote that a living organism, “dying, living and collapsing, gives its atoms to it and continuously takes them from it, but a living substance embraced by life always has a beginning in the living.” The second type of reproduction is also necessarily inherent in all life on Earth. Science has proven with sufficient certainty that the direct generation of living things from non-living matter is impossible at this stage of the Earth’s development.

After the emergence and spread of life on Earth, its emergence today on the basis of inorganic matter alone is no longer possible. All living systems existing on Earth now arise either on the basis of living things, or through the mediation of living things. Thus, before a living organism reproduces itself materially and energetically, it must be reproduced biologically, that is, be born by another living organism. The reproduction of living things by living things is, first of all, the transfer from one generation to another of genetic material, which determines the appearance of a certain morphophysiological structure in the offspring. It is clear that genetic material is not transmitted from generation to generation by itself; its transmission is also a function of human life.

Conclusion.

Genetics is the science of heredity and variability of organisms. Genetics is a discipline that studies the mechanisms and patterns of heredity and variability of organisms, and methods for controlling these processes. It is intended to reveal the laws of reproduction of living things through generations, the emergence of new properties in organisms, the laws of individual development of an individual and the material basis of historical transformations of organisms in the process of evolution. The objects of genetics are viruses, bacteria, fungi, plants, animals and humans. Against the background of species and other specificities, general laws are revealed in the phenomena of heredity for all living beings. Their existence shows the unity of the organic world.

In modern society, genetic issues are widely discussed in different audiences and from different points of view, including ethical ones, obviously for two reasons.

Firstly, genetics affects the most primary properties of living nature, as if key positions in life manifestations. Therefore, the progress of medicine and biology, as well as all expectations from it, often focus on genetics. In many ways, this focus is justified.

Secondly, in recent decades genetics has been developing so rapidly that it gives rise to both scientific and pseudo-scientific promising forecasts. This is especially true for human genetics, the progress of which raises ethical issues more acutely than in other areas of biomedical science.

In human genetics, the direct connection of scientific research with ethical issues is clearly visible, as well as the dependence of scientific research on the ethical meaning of their final results. Genetics has advanced so much that man is on the threshold of such power that allows him to determine his biological destiny. That is why the use of all the potential possibilities of genetics is possible only with strict adherence to ethical standards.

Genetics occupies a very important place in the system of modern sciences, and, perhaps, the most important achievements of the last decade of the past century are associated precisely with genetics. Now, at the beginning of the 21st century, prospects are opening up before humanity that captivate the imagination. Will scientists be able to realize the gigantic potential inherent in genetics in the near future? Will humanity receive the long-awaited deliverance from hereditary diseases, will man be able to prolong his too short life and gain immortality? At present we have every reason to hope for this.

Bibliographic list of used literature:

Artyomov A. What is a gene. - Taganrog: Publishing house “Red Page”, 1989.

Biological encyclopedic dictionary. - M.: Sov. encyclopedia, 1989.

Vernadsky V.I. Chemical structure of the Earth’s biosphere and its environment. - M.: Nauka, 1965.

1. living... who are aimed at development And reproduction relationships with certain... population ecology and genetics, mathematical genetics. “New... Therefore these three basic Problems and demand...

2. Genetics. Lecture notes

   Abstract >> Biology

   ... role genetics V development medicine. Main sections of modern genetics are: cytogenetics, molecular genetics, mutagenesis, population, evolutionary and ecological genetics ...

7. Features of reproduction and transmission of genetic information in bacteria and viruses. Sexduction, transformation, transduction.

8. Eukaryotic microorganisms as objects of genetics, features of the transmission of genetic information in them (tetrad analysis, gene conversion, parasexual cycle).

10. Evolution of ideas about the gene. Gene in the classical sense. Chemical nature of the gene. Fine structure of the gene.

11. Experimental decoding of the genetic code.

12. Genetic code and its basic properties.

13. Molecular mechanisms for the implementation of genetic information. Protein synthesis in the cell.

14. Genetic basis of ontogenesis, mechanisms of differentiation.

15. Auxotrophic mutants and their significance in elucidating biosynthesis chains. The “one gene, one enzyme” hypothesis.

16. Peculiarities of inheritance in monohybrid crossing. The hypothesis of gamete purity and its cytological basis.

17. Inheritance in polyhybrid crossing. The law of independent inheritance of characteristics and its cytological foundations.

18. Interaction of allelic genes. Multiple alleles.

19. Inheritance through the interaction of non-allelic genes.

20 Genetics of sex. Mechanisms of sex determination. Inheritance of sex-linked traits.

21. Gene linkage and crossing over (T. Morgan’s law).

22. Cytological evidence of crossing over.

23. Genetic and cytological maps of chromosomes.

24. Nonchromosomal inheritance and its main features.

25. Inheritance in a panmictic population. Hardy-Weinberg Law.

26. Factors of genetic dynamics of populations.

27. Population of self-fertilizing organisms, its genetic structure and dynamics.

28. Genetic basis of evolution.

29. Variability, its causes and methods of study.

30. Variability as a material for creating new breeds of animals, plant varieties and strains of microorganisms.

31. Modification variability and its significance in evolution and selection.

33. Spontaneous and induced mutagenesis.

34. Gene mutations. Methods for accounting for mutations.

35 Mutagens, their classification and characteristics. Genetic danger of environmental pollution with mutagens.

36. Chromosomal rearrangements, their types and role in evolution

37. Features of meiosis in heterozygotes for various chromosomal rearrangements.

38. Autopolyploids and their genetic characteristics.

39. Allopolyploids and their genetic characteristics. Synthesis and resynthesis of species.

40. Aneuploids, their types and genetic characteristics. Aneuploidy in humans.

Forms of aneuploidy

41. Man as an object of genetics. Methods for studying human genetics.

43. Human chromosomal diseases and the causes of their occurrence. Characteristics of the main chromosomal diseases.

Diseases caused by a violation of the number of autosomes (non-sex) chromosomes

Diseases associated with a violation of the number of sex chromosomes

Diseases caused by polyploidy

Chromosome structure disorders

44. Problems of medical genetics.

45. The role of heredity and environment in training and education.

46. ​​Selection as a science. The doctrine of the source material.

47. The doctrine of N.I.Vavilov about the centers of origin of cultivated plants and the law of homological series. The significance of the law of homological series for selection.

48. Crossbreeding systems in selection.

50. Heterosis and hypotheses about its mechanism. Use of heterosis in breeding.

51. Cytoplasmic male sterility and its use in selection.

52. Genetic, cellular and chromosome engineering.

Chromosome engineering.

49. Selection methods in breeding. Mass and individual selection. Family selection and the method of halves.

44. Problems of medical genetics.

Medical genetics(or human genetics, clinical genetics, genopathology) - a field of medicine, a science that studies the phenomena of heredity and variability in various human populations, features of the manifestation and development of normal and pathological signs, the dependence of diseases on genetic predisposition and environmental conditions. The task of honey Genetics is the identification, study, prevention and treatment of hereditary diseases, the development of ways to prevent the impact of negative environmental factors on human heredity. Medical genetics is an important branch of modern genetics that studies the role of hereditary factors in the occurrence of pathological symptoms and signs in the human body. Man, as an object of genetic research, is complex and at the same time convenient. The difficulty is associated with the existence of a number of limitations that arise when conducting a scientific experiment. For example, the experimental hybridization method is absolutely inapplicable to humans; simultaneous examination of representatives of three or more generations of a family is not always possible, etc. On the other hand, the rapid development of molecular and cellular biology has significantly expanded our understanding of the biochemical, physiological, molecular and other important processes occurring in the body of a healthy person, which allows us to judge the subtle pathogenetic mechanisms of individual clinical symptoms and diseases. It is known that hereditary diseases are part of the general hereditary variability of humans as a biological species, ensuring its evolution and adaptation to changing environmental conditions. In addition, there are quite a few human populations characterized by high levels of inbreeding and isolation. The study of such populations makes it possible to judge the mechanisms of the spread of mutant genes and the maintenance of their frequency at a certain level from generation to generation. The task of medical genetics is to identify, study, prevent and treat hereditary diseases, as well as to develop ways to prevent the harmful effects of environmental factors on human heredity.

45. The role of heredity and environment in training and education.

The genetic potential of a person is limited in time, and quite strictly. If you miss the deadline for early socialization, it will fade away before it has time to be realized. A striking example of this statement are the numerous cases when infants, by force of circumstances, ended up in the jungle and spent several years among animals. After their return to the human community, they could no longer fully catch up with what they had lost: master speech, acquire quite complex skills of human activity, their mental functions of a person developed poorly. This is evidence that the characteristic features of human behavior and activity are acquired only through social inheritance, only through the transmission of a social program in the process of upbringing and training.

To understand the role of heredity and environment in human ontogenesis, concepts such as “genotype” and “phenotype” are important.

Genotype- this is the hereditary basis of the organism, a set of genes localized in its chromosomes, this is the genetic constitution that the organism receives from its parents.

Phenotype- the totality of all the properties and characteristics of an organism formed in the process of its individual development. The phenotype is determined by the interaction of the organism with the environmental conditions in which its development occurs. Unlike the genotype, the phenotype changes throughout the life of the organism and depends on the genotype and environment. Identical genotypes (in identical twins), when placed in different environments, can produce different phenotypes. Taking into account all the influencing factors, the human phenotype can be represented as consisting of several elements.

These include: biological inclinations encoded in genes; environment (social and natural); individual activity; mind (consciousness, thinking).

Based on the complex structure of the human phenotype, we can say that the subject of eugenics is only one - the first of these elements. Representatives of eugenics absolutize it. At the same time, the social elements of the human phenotype remain outside their field of vision. This is the limitation of the position of the followers of this theory.

The interaction of heredity and environment in human development plays an important role throughout his life. But it acquires particular importance during the periods of formation of the body: embryonic, breast, childhood, adolescence and youth. It is at this time that an intensive process of development of the body and formation of personality is observed.

Heredity determines what an organism can become, but a person develops under the simultaneous influence of both factors - heredity and environment. Today it is becoming generally accepted that human adaptation is carried out under the influence of two programs of heredity: biological and social. All signs and properties of any individual are the result of the interaction of his genotype and environment. Therefore, each person is both a part of nature and a product of social development.

Most scientists today agree with this position. Disagreement arises when it comes to the role of heredity and environment in the study of human mental abilities. Some believe that mental abilities are inherited genetically, others say that the development of mental abilities is determined by the influence of the social environment.

Precisely defining the concept of “mental ability” is also a rather difficult task. Intellectual abilities are very diverse and unique. A person can be a brilliant chess player and a bad artist (poet, mathematician, etc.), and vice versa. But even the procedure for using tests to determine IQ has its drawbacks, which many scientists note. For example, when determining IQ, much depends on taking into account the social environment, the level and nature of the subjects’ upbringing and education, their organization, attentiveness, composure, and even temperament. Test results also depend not only on the subjects, but also on the testers - what questions are asked, for what purpose, from what area or activity, etc. It turns out that if children who were brought up on the street are asked a question about how to behave in society, and the children of aristocrats are asked, for example, about the rules of fist fighting, then probably the IQ of both will be low and in much the same.

Thus, it is quite difficult to obtain comprehensive information about people’s mental abilities using IQ. “Nevertheless,” notes A.P. Pekhov, “a large number of independent studies carried out in almost 10 countries indicate that individual differences in IQ are due to both heredity and environment.” At the same time, the author refers to studies by American scientists who determined the IQ of identical twins raised together and separately, i.e. in the same and different environments. It turned out that for twins raised separately, the differences between the coefficients were greater than for twins living together. Because The genotype of identical twins is identical; the results obtained indicate a significant influence of the environment on the mental development of the individual. The fact that mental abilities are determined not only by heredity, but also by environment, is confirmed by other studies.

Speaking about the biological inheritance of a person, it should be borne in mind that not only positive inclinations, but also mental inferiority are often determined by genotype. So, if one of the identical twins, who, as already noted, has almost the same genotype, develops schizophrenia, then in 69% the other one also develops it. In the case of dementia in one, in 97% this illness manifests itself in the other, while in fraternal twins - only in 37%. A high percentage of mentally retarded people are born when one or both parents are mentally retarded. When studying the pedigree of children with mental retardation, it turned out that even in cases where the parents were completely normal, they had relatives with similar diseases.

PROBLEMS OF GENETICS

Genetics- the science of heredity and variability of organisms and methods of controlling them.

1900 - rediscovery of Mendel's laws. The emergence of genetics is associated with the discovery of the laws of heredity by Mendel in 1865. But Mendel's work went unnoticed. In 1900, Mendel's laws were discovered independently by 3 scientists (De Vries, Chermak, Correns).

In the 20th century, a number of discoveries followed, namely, in 1912, Morgan developed the chromosomal theory of heredity; in 1944, American biochemists Avery and company established that DNA is the carrier of hereditary information; in 1953, the structure of DNA was deciphered, which showed that the molecule consists of 2 polynucleide chains, each of which acts as a template for the synthesis of new chains. In recent decades, scientists have established the dependence of protein synthesis on the state of genes, carried out gene synthesis, deciphered the amino acid sequence of many proteins, etc.

At the end of 2000, the human genome was deciphered. Genome - a set of genes concentrated in a single set of chromosomes of a given organism. The human genome contains about 100 thousand genes containing about 3 billion pieces of information.

This has provided an understanding of the causes and mechanisms of diseases and will allow us to develop effective methods for treating them.

But it takes a lot of time to establish the functions of all genes.

The largest discovery of modern genetics is related to the establishment of the abilities of genes.

Mutations are abrupt and stable changes in genetic material that is inherited.

Based on changes in genetic material, mutations are divided into:

1. Genomic - change in the number of chromosomes. The loss of any of the 46 chromosomes or the addition of an extra one leads to severe developmental disorders. For example, an extra chromosome in pair 21 leads to Down syndrome.

2. Chromosomal. Associated with changes in the structure of the child’s germ cells.

3. Gene mutations are associated with changes in the molecular structure of DNA.

Mutations can be harmful, neutral, and much less often - beneficial (increased adaptability to life).

Factors that cause mutations are called mutagenic: radiation, chemical changes, temperature changes, viruses, bacteria.

GENETIC ENGINEERING

It arose in the 70-80s of the 20th century. Genetic engineering is a branch of molecular genetics associated with the targeted construction of new combinations of genes that do not exist in nature.

TASKS OF GENETIC ENGINEERING: deciphering the structure of genes, synthesizing genes by biochemical means, cloning genes, transferring isolated or newly synthesized genes from one cell or organism to another with the aim of purposefully changing their hereditary properties, i.e. management of heredity. Through human intervention in the design of DNA, the properties of dozens of animals and plants have been improved or altered to increase crop yields and improve livestock breeds.

APPLICATION OF GENETIC ENGINEERING: in medicine1. associated with the diagnosis of diseases - diagnostic drugs have been developed to detect genetic abnormalities during pregnancy. 2. treatment of diseases. Methods are being developed to treat hereditary diseases by introducing genes with the correct information into cells containing defective genes or by adding new genes that contain substances to fight the disease (gene therapy).

3. Prevention. One of the promising areas of genetic engineering is the cultivation of genes from sick and healthy people in the cells of other living organisms in order to study the molecular basis of hereditary human diseases.

Cloning is a process in which a living being is produced from a single cell taken from another living being.

Genetic engineering lies at the heart of modern biotechnology.

APPLICATION: in medicine and pharmaceuticals (growth hormone, interferon, cloned insulin gene, neuropyptids - brain proteins that regulate biological processes such as sleep, memory, pain, etc.), production of food products from transgenic plants (genetically modified with specified parameters ).

Since 1996, transgenic potatoes, corn, and soybeans have been grown, however, not all scientists are confident in their safety.