In 1920 N.I. Vavilov outlines the main ideas of the Law of Homologous Series in a report at the III All-Russian Selection Congress in Saratov. Main idea: related plant species have similar spectra of variation (often a fixed number of strictly defined variations).
“And Vavilov did such a thing. He collected all the known hereditary characteristics from the best studied, as I already said, plants from among the cultivated cereals, arranged them in a certain order in tables and compared all the subspecies, forms and varieties known to him at that time. A lot of tables were compiled, of course, there was a huge amount of material. At the same time, back in Saratov, he added legumes to cereals - various peas, vetches, beans, beans, etc. - and some other cultivated plants. And in many cases there was parallelism in many species. Of course, each family, genus, and species of plants had their own characteristics, their own form, their own way of expression. For example, the color of seeds varied from almost white to almost black in almost all cultivated plants. This means that if better studied cereals with a huge number of already known, studied varieties and forms have several hundred different characteristics described, but other, less studied or wild relatives of cultivated species do not have many characteristics, then they can, so to speak, be predicted. They will be found in the corresponding large material.
Vavilov showed that, in general, the hereditary variability of all plants varies to a very large extent in parallel. He called this the homologous series of plant variability. And he pointed out that the closer the species are to each other, the greater the homology of the series of character variability. A number of different general patterns have been identified in these homologous series of hereditary variability in plants. And this circumstance was taken by Vavilov as one of the most important foundations for further selection and search for economically useful traits in plants introduced into cultivation. The study of homologous series of hereditary variability, first of all in cultivated plants, then in domestic animals, is now self-evident, one of the foundations for further selection of varieties of certain types of plants being studied that are needed by humans. This was, perhaps, one of Vavilov’s first major achievements on a global scale, which very quickly created his worldwide name. The name of, if not the first and best, then one of the first and best applied botanists in the world.
In parallel with this, Vavilov made a large number of expeditions around the world - throughout Europe, most of Asia, throughout much of Africa, North, Central and South America - collecting enormous material, mainly on cultivated plants. In 1920, I think, Vavilov was made director of the Bureau of Applied Botany and New Crops. This Bureau was slightly changed and turned into the Institute of Applied Botany and New Crops, then the Institute of Applied Botany, Genetics and Plant Breeding. And by the end of the 30s it had already become the All-Union Institute of Plant Growing. This name has still been preserved, although its global share, of course, fell greatly after the death of Vavilov. But still, many Vavilov traditions are still maintained, and part of the huge world living collection of varieties, subspecies and forms of cultivated plants from literally all groups of plants cultivated on the globe is preserved in Pushkin, the former Detskoye Selo, the former Tsarskoe Selo. This is a living museum, replanted every year, created by Vavilov. The same is true at countless experimental stations scattered throughout the Soviet Union.
During his numerous trips, Vavilov again managed not to drown in the enormous material, in this case the geographical diversity of forms of various types of cultivated plants. He plotted everything on large-scale maps with multi-colored pencils, first playing with geographic maps like little children, and then translating it all into relatively simple small maps with black icons of various types for different forms of cultivated plants. So he discovered in the world, on the globe, in the biosphere of our planet, several centers of cultural plant diversity. And he showed, simply on maps, the spreading, distribution on Earth not only of individual species, but of certain groups of species, domesticated, apparently, for the first time in a certain place, well, say, in Northern or Central China or in the mountainous part of North Africa, or , say, in the region of Peru, in South America, in the mountains, in the Andes. From there, usually not just one species of some cultivated plant, but a group of economically related species that arose as cultivated plants and took root as cultivated plants in a certain place, spread across the Earth. Some are not far, a short distance, while others have conquered half the world, as they say, like the same wheat or peas.
Vavilov thus established centers of diversity and origin of various forms of cultivated plants in different places on the globe. And he created a whole theory of the origin of cultivated plants in various eras of the ancient and ancient world. This was Vavilov’s second great achievement, again a worldwide one. Now it is impossible to further develop the history of world agriculture and the history of the centers of origin of cultivated plants without the foundation created by Vavilov. There are attempts, so to speak, at some reform and modification of Vavilov’s views, but we can say that these are particularities in comparison with the general world picture created by Vavilov.
This means that I have already listed three huge achievements: plant immunity, the law of homological series and the theory of agricultural centers and the emergence of various forms of cultivated plants. Perhaps the last thing I would like to name from Vavilov’s general achievements is a large number of his works and efforts, mainly efforts in the sense of propaganda at various congresses, international and all-Union, writing popular science articles on the problem of promoting agriculture to the north in the first place and in areas occupied by deserts and wastelands, combined with nature conservation in a completely modern and even intended for the near future sense: the promotion of culture together with a reasonable attitude towards the communities of living organisms of the biosphere. In these areas, Vavilov is absolutely exceptional, I would say, an exceptionally great scientist on a global scale.”
Homologous series in hereditary variability law, open Russian geneticist N.I. Vavilov in 1920, a pattern establishing parallelism (similarity) in hereditary (genotypic) variability in related organisms. In Vavilov’s formulation, the law states: “Species and genera that are genetically close to each other are characterized by identical series of hereditary variability with such regularity that, knowing the series of forms for one species, one can predict the presence of identical forms in other species and genera.” Moreover, the closer the relationship between species, the more complete the similarity (homology) in the series of their variability. The law summarizes a huge amount of material on the variability of plants (cereals and other families), but it also turned out to be valid for the variability of animals and microorganisms.
The phenomenon of parallel variability in closely related genera and species is explained by their common origin and, therefore, the presence in a significant part of them of identical genes, obtained from a common ancestor and not changed in the process. When mutated, these genes produce similar characteristics. Parallelism in genotypic variability in related species is manifested by parallelism in phenotypic variability, i.e., similar characteristics (phenotypes).
Vavilov’s law is a theoretical basis for choosing directions and methods for obtaining economically valuable traits and properties in cultivated plants and domestic animals.
N.I. Vavilov, studying hereditary variability in cultivated plants and their ancestors, discovered a number of patterns that made it possible to formulate the law of homological series of hereditary variability: “Species and genera that are genetically close are characterized by similar series of hereditary variability with such correctness that, knowing a number of forms within one species, one can foresee the finding of parallel forms in other species and genera. The closer the genera and species are genetically located in the general system, the more complete the similarity in the series of their variability. Whole families of plants are generally characterized by a certain cycle of variation passing through all the genera and species that make up the family 30.”
This law can be illustrated by the example of the Poa family, which includes wheat, rye, barley, oats, millet, etc. Thus, the black color of the caryopsis was found in rye, wheat, barley, corn and other plants, and the elongated shape of the caryopsis was found in all studied species of the family. The law of homological series in hereditary variability allowed N.I. Vavilov himself to find a number of forms of rye, previously unknown, based on the presence of these characteristics in wheat. These include: awned and awnless ears, grains of red, white, black and purple color, mealy and glassy grains, etc.
The law discovered by N.I. Vavilov is valid not only for plants, but also for animals. Thus, albinism occurs not only in different groups of mammals, but also in birds and other animals. Short-fingeredness is observed in humans, cattle, sheep, dogs, birds, the absence of feathers in birds, scales in fish, wool in mammals, etc.
The law of homologous series of hereditary variability is of great importance for breeding practice. It allows us to predict the presence of forms not found in a given species, but characteristic of closely related species, that is, the law indicates the direction of searches. Moreover, the desired form can be found in the wild or obtained through artificial mutagenesis. For example, in 1927, the German geneticist E. Baur, based on the law of homological series, suggested the possible existence of an alkaloid-free form of lupine, which could be used as animal feed. However, such forms were not known. It has been suggested that alkaloid-free mutants are less resistant to pests than bitter lupine plants, and most of them die before flowering.
Based on these assumptions, R. Zengbusch began the search for alkaloid-free mutants. He examined 2.5 million lupine plants and identified among them 5 plants with a low content of alkaloids, which were the ancestors of fodder lupine.
Later studies showed the effect of the law of homological series at the level of variability of morphological, physiological and biochemical characteristics of a wide variety of organisms - from bacteria to humans.
Artificial mutations
Spontaneous mutagenesis occurs constantly in nature. However, spontaneous mutations are rare. For example, in Drosophila, the white eye mutation is formed with a frequency of 1:100,000 gametes; in humans, many genes mutate with a frequency of 1:200,000 gametes.In 1925, G.A. Nadson and G.S. Filippov discovered the mutagenic effect of radium rays on hereditary variability in yeast cells. Of particular importance for the development of artificial mutagenesis were the works of G. Meller (1927), who not only confirmed the mutagenic effect of radium rays in experiments on Drosophila, but also showed that irradiation increases the frequency of mutations hundreds of times. In 1928, L. Stadler used X-rays to produce mutations. Later, the mutagenic effect of chemicals was also proven. These and other experiments showed the existence of a large number of factors called mutagenic, capable of causing mutations in various organisms.
All mutagens used to produce mutations are divided into two groups:
physical - radiation, high and low temperature, mechanical impact, ultrasound;
chemical- various organic and inorganic compounds: caffeine, mustard gas, heavy metal salts, nitrous acid, etc.
Induced mutagenesis is of great importance. It makes it possible to create valuable source material for breeding, hundreds of highly productive varieties of plants and animal breeds, increase the productivity of a number of producers of biologically active substances by 10-20 times, and also reveals ways to create means of protecting humans from the action of mutagenic factors.
Vavilov's law of homological series
An important theoretical generalization of N. I. Vavilov’s research is the doctrine of homological series he developed. According to the law of homological series of hereditary variability formulated by him, not only genetically close species, but also genera of plants form homological series of forms, i.e., there is a certain parallelism in the genetic variability of species and genera. Close species, due to the great similarity of their genotypes (almost the same set of genes), have similar hereditary variability. If all known variations of characters in a well-studied species are placed in a certain order, then almost all the same variations in character variability can be found in other related species. For example, the variability of ear spinality is approximately the same in soft, durum wheat and barley.
Interpretation by N.I. Vavilov. Species and genera that are genetically close are characterized by similar series of hereditary variability, with such regularity that, knowing the series of forms within one species, one can predict the presence of parallel forms in other species and genera. The closer the relationship, the more complete the similarity in the series of variability.
Modern interpretation of the law
Related species, genera, families have homologous genes and gene orders in chromosomes, the similarity of which is the more complete, the closer the taxa being compared are evolutionarily closer. The homology of genes in related species is manifested in the similarity of the series of their hereditary variability (1987).
Meaning of the law
1. The law of homological series of hereditary variability makes it possible to find the necessary characteristics and variants in the almost infinite variety of forms of various species of both cultivated plants and domestic animals, and their wild relatives.
2. It makes it possible to successfully search for new varieties of cultivated plants and breeds of domestic animals with certain required characteristics. This is the enormous practical significance of the law for crop production, livestock breeding and breeding.
3. Its role in the geography of cultivated plants is comparable to the role of D. I. Mendeleev’s Periodic Table of Elements in chemistry. By applying the law of homological series, it is possible to establish the center of origin of plants according to related species with similar characteristics and forms, which probably develop in the same geographical and ecological environment.
Ticket 4
Inheritance of characteristics during divergence of sex chromosomes (primary and secondary nondisjunction of X chromosomes in Drosophila)
As noted earlier, when a white-eyed female Drosophila is crossed with a red-eyed male F1 all the daughters have red eyes, and all the sons who receive their only X-chromosome from mother, eyes white. However, sometimes in such crossings single red-eyed males and white-eyed females appear, the so-called exceptional flies with a frequency of 0.1-0.001%. Bridges suggested that the appearance of such “exceptional individuals” is explained by the fact that in their mother, during meiosis, both X chromosomes ended up in one egg, i.e. non-divergence occurred X-chromosomes. Each of these eggs can be fertilized either by sperm or X-chromosome, or Y-chromosome. As a result, 4 types of zygotes can be formed: 1) with three X-chromosomes – XXX; 2) with two mothers X-chromosomes and Y-chromosome XXY; 3) with one paternal X-chromosome; 4) without X-chromosomes, but with Y-chromosome.
XXY are normal fertile females. XO- males, but sterile. This shows that in Drosophila Y-chromosome does not contain sex-determining genes. When crossing XXY females with normal red-eyed males ( XY) Bridges found among the offspring 4% white-eyed females and 4% red-eyed males. The rest of the offspring consisted of red-eyed females and white-eyed males. The author explained the appearance of such exceptional individuals by secondary nondivergence X-chromosomes in meiosis, because the females taken in the cross ( XXY), arose as a result of primary chromosome nondisjunction. Secondary chromosome nondisjunction in such females in meiosis is observed 100 times more often than primary.
In a number of other organisms, including humans, nondisjunction of sex chromosomes is also known. Of the 4 types of offspring resulting from nondivergence X-chromosomes in women, individuals who do not have any X-chromosomes die during embryonic development. Zygotes XXX develop in women who are more likely to have mental defects and infertility than usual. From zygotes XXY defective men develop - Klinefelter syndrome - infertility, mental retardation, eunuchoid physique. Descendants from one X-chromosomes often die in embryonic development; the rare survivors are women with Shereshevsky-Turner syndrome. They are short, childish, and sterile. In humans Y-chromosomes contain genes that determine the development of a male organism. With absence Y-Chromosomes develop according to the female type. Nondisjunction of sex chromosomes occurs more frequently in humans than in Drosophila; On average, for every 600 boys born, there is one with Klinefelter syndrome.
Among the flora of the globe, there is a significant number (more than 2500) species of a group of plants cultivated by humans and called cultural. Cultivated plants and the agrophytocenoses formed by them replaced meadow and forest communities. They are the result of human agricultural activity, which began 7-10 thousand years ago. Wild plants that become cultivated inevitably reflect a new stage in their life. The branch of biogeography that studies the distribution of cultivated plants, their adaptation to soil-climatic conditions in various regions of the globe and includes elements of agricultural economics is called geography of cultivated plants.
According to their origin, cultivated plants are divided into three groups:
- the youngest group
- weed species,
- the most ancient group.
Youngest group cultivated plants come from species that still live in the wild. These include fruit and berry crops (apple, pear, plum, cherry), all melons, and some root crops (beets, rutabaga, radishes, turnips).
Weed species plants became objects of culture where the main crop produced low yields due to unfavorable natural conditions. Thus, with the advancement of agriculture to the north, winter rye replaced wheat; The oilseed crop camelina, widespread in Western Siberia and used to produce vegetable oil, is a weed in flax crops.
For most ancient cultivated plants cannot be established when their cultivation began, since their wild ancestors have not been preserved. These include sorghum, millet, peas, beans, beans, and lentils.
The need for source material for breeding and improving varieties of cultivated plants led to the creation of the doctrine of their centers of origin. The teaching was based on Charles Darwin’s idea of the existence geographical centers of origin of biological species. The geographical areas of origin of the most important cultivated plants were first described in 1880 by the Swiss botanist A. Decandolle. According to his ideas, they covered quite vast territories, including entire continents. The most important research in this direction, half a century later, was carried out by the remarkable Russian geneticist and botanist-geographer N.I. Vavilov, who studied the centers of origin of cultivated plants on a scientific basis.
N.I. Vavilov proposed a new one, which he called differentiated, a method for establishing the original center of origin of cultivated plants, which is as follows. A collection of the plant of interest collected from all places of cultivation is studied using morphological, physiological and genetic methods. Thus, the area of concentration of the maximum diversity of forms, characteristics and varieties of a given species is determined.
The doctrine of homological series. An important theoretical generalization of N. I. Vavilov’s research is the doctrine of homological series he developed. According to the law of homological series of hereditary variability formulated by him, not only genetically close species, but also genera of plants form homological series of forms, i.e., there is a certain parallelism in the genetic variability of species and genera. Close species, due to the great similarity of their genotypes (almost the same set of genes), have similar hereditary variability. If all known variations of characters in a well-studied species are placed in a certain order, then almost all the same variations in character variability can be found in other related species. For example, the variability of ear spinality is approximately the same in soft, durum wheat and barley.
Interpretation by N. I. Vavilov. Species and genera that are genetically close are characterized by similar series of hereditary variability, with such regularity that, knowing the series of forms within one species, one can predict the presence of parallel forms in other species and genera. The closer the relationship, the more complete the similarity in the series of variability.
Modern interpretation of the law. Related species, genera, families have homologous genes and gene orders in chromosomes, the similarity of which is the more complete, the closer the taxa being compared are evolutionarily closer. The homology of genes in related species is manifested in the similarity of the series of their hereditary variability (1987).
The meaning of the law.
- The law of homological series of hereditary variability makes it possible to find the necessary characteristics and variants in the almost infinite variety of forms of various species of both cultivated plants and domestic animals, and their wild relatives.
- It makes it possible to successfully search for new varieties of cultivated plants and breeds of domestic animals with certain required characteristics. This is the enormous practical significance of the law for crop production, livestock breeding and breeding.
- Its role in the geography of cultivated plants is comparable to the role of D. I. Mendeleev’s Periodic Table of Elements in chemistry. By applying the law of homological series, it is possible to establish the center of origin of plants according to related species with similar characteristics and forms, which probably develop in the same geographical and ecological environment.
Geographical centers of origin of cultivated plants. For the emergence of a large center of origin of cultivated plants, N.I. Vavilov considered a necessary condition, in addition to the richness of wild flora in species suitable for cultivation, the presence of an ancient agricultural civilization. The scientist came to the conclusion that the vast majority of cultivated plants are connected by 7 main geographical centers of their origin:
- South Asian tropical,
- East Asian,
- South-West Asian,
- Mediterranean,
- Ethiopian,
- Central American,
- Andean.
Outside these centers there was a significant territory that required further study in order to identify new centers of domestication of the most valuable representatives of wild flora. The followers of N.I. Vavilov - A.I. Kuptsov and A.M. Zhukovsky continued research into the study of the centers of cultivated plants. Ultimately, the number of centers and the territory they covered increased significantly, there were 12 of them
- Sino-Japanese.
- Indonesian-Indochine.
- Australian.
- Hindustan.
- Central Asian.
- Near Asian.
- Mediterranean.
- African.
- European-Siberian.
- Central American.
- South American.
- North American