The essence of the law of homologous series of hereditary variability. Homological series of hereditary variability

Mutations that occur naturally without affecting the body of various factors are called spontaneous. The main feature of the manifestation of spontaneous mutations is that genetically close species and genera are characterized by the presence of similar forms of variability. The pattern of the presence of homologous series in hereditary variability was established by the outstanding geneticist and breeder, Academician N.I. Vavilov (1920). He found that homologous series exist not only at the species and genus levels in plants, but can also be found in mammals and humans.

The essence of the law is that genetically close genera and species are characterized by homologous (similar) series in hereditary variability. Similar genotypic variability is based on a similar genotype in closely related forms (i.e., a set of genes, their position in homologous loci). Therefore, knowing the forms of variability, for example, a number of mutations in species within the same genus, one can assume the presence of the same mutations in other species of a given genus or family. Similar mutations in genetically related species N.I. Vavilov called homologous series in hereditary variability. Examples:

1) representatives of the cereal family have a similar genotype. Similar mutations are observed within the genera of this family (wheat, rye, oats, etc.). These include the following: naked-grained, awnless, lodging, different consistency and color of grain, etc. Awnless forms of wheat, rye, oats, and rice are especially common;

2) similar mutations occur in humans and mammals: short-toed (sheep, humans), albinism (rats, dogs, humans), diabetes mellitus (rats, humans), cataracts (dogs, horses, humans), deafness (dogs, cats, humans) ) and etc.

The law of homological series of hereditary variability is universal. Medical genetics uses this law to study diseases in animals and develop treatments for them in humans. It has been established that oncogenic viruses are transmitted through germ cells, integrating into their genome. At the same time, the offspring develop comorbidities similar to those of the parents. The DNA nucleotide sequence has been studied in many closely related species, and the degree of similarity is more than 90%. This means that the same type of mutations can be expected in related species.

The law has wide application in plant breeding. Knowing the nature of hereditary changes in some varieties, it is possible to predict similar changes in related varieties by acting on them with mutagens or using gene therapy. In this way, beneficial changes can be brought about in them.

Modification variability(according to Ch. Darwin - a certain variability) - is a change in the phenotype under the influence of environmental factors that are not inherited, and the genotype remains unchanged.

Changes in the phenotype under the influence of environmental factors in genetically identical individuals are called modifications. Modifications are otherwise called changes in the degree of expression of a trait. The appearance of modifications is due to the fact that environmental factors (temperature, light, moisture, etc.) affect the activity of enzymes and, within certain limits, change the course of biochemical reactions. Modification variability is adaptive in nature, in contrast to mutational variability.

Modification examples:

1) the arrowhead has 3 types of leaves, differing in shape, depending on the action environmental factor: arrow-shaped, located above the water, oval - on the surface of the water, linear - immersed in water;

2) in a Himalayan rabbit, in place of shaved white wool, when it is placed in new conditions (temperature 2 C), black hair grows;

3) when using certain types of feed, body weight and milk yield of cows increase significantly;

4) lily of the valley leaves on clay soils are wide, dark green, and on poor sandy soils they are narrow and pale in color;

5) Dandelion plants relocated high up in the mountains, or in areas with a cold climate, do not reach normal sizes, and grow dwarfed.

6) with an excess content of potassium in the soil, plant growth increases, and if there is a lot of iron in the soil, then a brownish tint appears on the white petals.

Mod properties:

1) modifications can occur in a whole group of individuals, because these are group changes in the severity of signs;

2) the changes are adequate, i.e. correspond to the type and duration of exposure to a certain environmental factor (temperature, light, soil moisture, etc.);

3) modifications form a variation series, therefore they are referred to as quantitative changes in features;

4) modifications are reversible within one generation, i.e. with a change in external conditions in individuals, the degree of expression of signs changes. For example, in cows with a change in feeding, milk yield may change, in humans, under the influence of ultraviolet rays, a tan, freckles, etc. appear;

5) modifications are not inherited;

6) modifications are adaptive (adaptive) in nature, i.e., in response to changes in environmental conditions, individuals exhibit phenotypic changes that contribute to their survival. For example, domestic rats adapt to poisons; hares change seasonal color;

7) are grouped around the average value.

Under the influence of the external environment, more, the length and shape of the leaves, height, weight, etc.

However, under the influence of the environment, signs can change within certain limits. reaction rate are the upper and lower bounds within which the attribute can change. These limits, in which the phenotype can change, are determined by the genotype. Example 1: milk yield from one cow is 4000–5000 l / year. This indicates that the variability of this trait is observed within such limits, and the reaction rate is 4000–5000 L/year. Example 2: if the height of the stem of a tall oat variety varies from 110 to 130 cm, then the reaction rate of this trait is 110–130 cm.

Different signs have different norms of reaction - wide and narrow. Wide reaction rate- leaf length, body weight, milk yield of cows, etc. Narrow reaction rate- the fat content of milk, the color of seeds, flowers, fruits, etc. Quantitative signs have a wide reaction rate, and qualitative ones have a narrow reaction rate.

Statistical analysis of modification variability on the example of the number of spikelets in an ear of wheat

Since modification is a quantitative change in a trait, it is possible to perform a statistical analysis of modification variability and derive the average value of modification variability, or a variation series. Variation series variability of the trait (i.e., the number of spikelets in the ears) - the arrangement in a row of ears according to the increase in the number of spikelets. The variational series consists of separate variants (variations). If we count the number of individual variants in the variation series, we can see that the frequency of their occurrence is not the same. Options ( variations) is the number of spikelets in ears of wheat (single expression of the trait). Most often, the average indicators of the variation series are found (the number of spikelets varies from 14 to 20). For example, in 100 ears, you need to determine the frequency of occurrence of different options. According to the results of calculations, it can be seen that most often there are spikes with an average number of spikelets (16–18):

The top row shows the options, from smallest to largest. The bottom row is the frequency of occurrence of each option.

The distribution of a variant in a variation series can be shown visually using a graph. The graphical expression of the variability of a trait is called variation curve, which reflects the limits of variation and the frequency of occurrence of specific variations of the trait (Fig. 36) .

V

Rice. 36 . Variation curve of the number of spikelets in an ear of wheat

In order to determine the average value of the modification variability of wheat ears, it is necessary to take into account the following parameters:

P is the number of spikelets with a certain number of spikelets (the frequency of occurrence of the trait);

n is the total number of series options;

V is the number of spikelets in an ear (options forming a variational series);

M - the average value of modification variability, or the arithmetic mean of the variation series of ears of wheat is determined by the formula:

M=–––––––––– (average value of modification variability)

2x14+7x15+22x16+32x17+24x18+8x19+5x20

M=––––––––––––––––––––––––––––––––––––––– = 17, 1 .

The average value of modification variability has a practical application in solving the problem of increasing the productivity of agricultural plants and animals.

Activities of N. I. Vavilov

The outstanding Soviet geneticist Nikolai Ivanovich Vavilov made a great contribution to the development of domestic science. A whole galaxy of prominent Russian scientists was brought up under his leadership. The studies carried out by N.I. Vavilov and his students made it possible for agricultural science to master new methods of searching for wild plant species as a starting material for breeding, laid the theoretical foundations of Soviet breeding.

Remark 1

Based on the huge amount of collected collection material, the doctrine of the centers of origin of cultivated plants was formulated. And the seed samples collected by Vavilov and his associates provided a wide front for genetic research and breeding work.

It was thanks to the analysis of the collected materials that the famous law of homological series was formulated.

The essence of the law of homologous series of hereditary variability

In the course of a long-term study of wild and cultivated forms of vegetation on five continents, N.I. Vavilov concluded that the variability of species and genera close in origin occurs in similar ways. In this case, the so-called series of variability are formed. These series of variability are so correct that, knowing a number of characters and forms within one species, one can foresee the presence of these qualities in other species and genera. The closer the relationship, the more complete the similarity in the series of variability.

For example, in watermelon, pumpkin and melon, the shape of the fruit can be oval, round, spherical, cylindrical. The color of the fruit may be light, dark, striped or spotted. The leaves of all three plant species can be entire or deeply dissected.

If we consider cereals, then out of $38$ of the studied traits characteristic of cereals:

• $37 was found in rye and wheat,
• barley and oats - $35$,
• for corn and rice - $32$,
• millet has $27.

Knowledge of these regularities makes it possible to foresee the manifestation of certain traits in some plants. On the example of the manifestation of these signs in other plants related to them.

IN modern interpretation the formulation of this law of homologous series of hereditary variability is as follows:

“Related species, genera, families have homologous genes and gene orders in chromosomes, the similarity of which is the more complete, the evolutionarily closer compared taxa.”

Vavilov established this regularity for plants. But subsequent research has shown that the law is universal.

The genetic basis of the law of homologous series of heredity

The genetic basis of the above-mentioned law is the fact that under similar conditions, closely related organisms can react in the same way to environmental factors. And their biochemical processes proceed in approximately the same way. This pattern can be formulated as follows:

"The degree of historical commonality of organisms is directly proportional to the number of common genes in the groups being compared."

Since the genotype of closely related organisms is similar, the changes in these genes during mutations can be similar. Outwardly (phenotypically), this manifests itself as the same character of variability in closely related species, genera, etc.

The meaning of the law of homologous series of heredity

The law of homological series is of great importance both for the development of theoretical science and for practical application in agricultural production. It gives the key to understanding the direction and ways of evolution of related groups of living organisms. In breeding, on its basis, they plan to create new varieties of plants and breeds of domestic animals with a certain set of characteristics, based on the study of the hereditary variability of related species.

In the taxonomy of organisms, this law makes it possible to find new expected forms of organisms (species, genera, families) with a certain set of features, provided that such a set was found in related systematic groups.

MUTATIONAL VARIABILITY

Plan

The difference between mutations and modifications.

Mutation classification.

Law of N.I. Vavilov

Mutations. The concept of mutation. mutagenic factors.

Mutations - These are sudden, persistent, natural or artificial changes in genetic material that occur under the influence of mutagenic factors .

Types of mutagenic factors:

BUT) physical– radiation, temperature, electromagnetic radiation.

B) chemical factors - substances that cause poisoning of the body: alcohol, nicotine, formalin.

IN) biological- viruses, bacteria.

The difference between mutations and modifications

Mutation classification

There are several classifications of mutations.

I Classification of mutations by value: beneficial, harmful, neutral.

Useful mutations lead to increased resistance of the organism and are the material for natural and artificial selection.

Harmful mutations reduce viability and lead to the development of hereditary diseases: hemophilia, sickle cell anemia.

II Classification of mutations by localization or place of occurrence: somatic and generative.

Somatic arise in the cells of the body and affect only part of the body, while individuals of the mosaic develop: different eyes, hair color. These mutations are inherited only during vegetative propagation (in currants).

Generative – occur in germ cells or in cells from which gametes are formed. They are divided into nuclear and extranuclear (mitochondrial, plastid).

III Mutations according to the nature of the change in the genotype: chromosomal, genomic, gene.

Genetic (or point) not visible under a microscope, are associated with a change in the structure of the gene. These mutations result from the loss of a nucleotide, the insertion or substitution of one nucleotide for another. These mutations lead to gene diseases: color blindness, phenylketonuria.

Chromosomal (perestroika) associated with changes in the structure of chromosomes. May happen:

Deletion: - loss of a chromosome segment;

Duplication - duplication of a chromosome segment;

Inversion - rotation of a part of the chromosome by 180 0 ;

Translocation - exchange of segments of nonhomologous chromosomes and merger two non-homologous chromosomes into one.

Causes of chromosomal mutations: the occurrence of two or more chromosome breaks and their subsequent connection, but in the wrong order.

Genomic mutations lead to a change in the number of chromosomes. Distinguish heteroploidy And polyploidy.

heteroploidy associated with a change in the number of chromosomes, on several chromosomes - 1.2.3. Causes: no segregation of chromosomes in meiosis:

- Monosomy - decrease in the number of chromosomes by 1 chromosome. The general formula of the chromosome set is 2n-1.

- Trisonomy - an increase in the number of chromosomes by 1. The general formula is 2n + 1 (47 chromosomes Clanfaiter's syndrome; trisonomy of 21 pairs of chromosomes - Down's syndrome (signs of multiple congenital malformations that reduce the viability of the body and impaired mental development).

Polyploidy - multiple change in the number of chromosomes. In polyploid organisms, the haploid (n) set of chromosomes in cells is repeated not 2 times, as in diploid ones, but 4-6 times, sometimes much more - up to 10-12 times.

The emergence of polyploids is associated with a violation of mitosis or meiosis. In particular, non-separation of homologous chromosomes during meiosis leads to the formation of gametes with an increased number of chromosomes. In diploid organisms, this process can produce diploid (2n) gametes.

It is widely found in cultivated plants: buckwheat, sunflower, etc., as well as in wild plants.

The law of N.I. Vavilov (the law of homologous series of hereditary variability).

/ Since ancient times, researchers have observed the existence of similar characters in different species and genera of the same family, for example, melons that look like cucumbers, or watermelons that look like melons. These facts formed the basis of the law of homologous series in hereditary variability.

Multiple allelism. Parallel variability. A gene can be in more than two states. The variety of alleles for a single gene is called multiple allelism. Different alleles determine different degrees of the same trait. The more alleles the individuals of populations carry, the more plastic the species is, the better adapted it is to changing environmental conditions.

Multiple allelism underlies parallel variability - a phenomenon in which similar characters appear in different species and genera of the same family. N.I. Vavilov systematized the facts of parallel variability./

N.I. Vavilov compared species of the Zlaki family. He found out that if soft wheat has winter and spring forms, awned and awnless, then the same forms are necessarily found in durum wheat. Moreover, the composition of features. By which forms differ within species and genus, it often turns out to be the same in other genera. For example, the forms of rye and barley repeat the forms of different types of wheat, while forming the same parallel or homologous series of hereditary variability.

The systematization of facts allowed N.I. Vavilov to formulate law of homologous series in hereditary variability (1920): species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity. That, knowing a number of forms within one species, it is possible to foresee the finding of parallel forms in other species and genera.

The homology of hereditary traits of closely related species and genera is explained by the homology of their genes, since they originated from the same parent species. In addition, the mutation process in genetically close species proceeds similarly. Therefore, they have similar series of recessive alleles and, as a result, parallel traits.

Derivation from Vavilov's law: each species has certain boundaries of mutational variability. No mutation process can lead to changes that go beyond the spectrum of hereditary variability of the species. So, in mammals, mutations can change the color of the coat from black to brown, red, white, striping, spotting may occur, but the appearance of a green color is excluded.

On June 4, he made a presentation "The law of homological series in hereditary variability." This is one of those works that are considered fundamental and are the theoretical basis for biological research. The essence of the law boils down to the fact that species and genera that are genetically close (connected to each other by the unity of origin) are characterized by similar series in hereditary variability. Student enthusiasm for the study of cereals, and then cruciferous, legumes, pumpkins, allowed Vavilov and his students to find mutations that are similar in related species, and then genera. In the table developed as a result of the experiments, Vavilov noted the mutations, the manifestation of which was found in these species, with a “+” sign, and empty spaces indicate that such mutations should be, but have not yet been detected. A table with empty cells that will be filled in with the further development of science. Where have we met with something like this? Of course, in chemistry, the famous periodic table! The regularity of the two laws is confirmed by science. "Empty" cells are filled, and this is the basis for practical selection. Durum wheat is known only in the spring form, but on the basis of the law, durum wheat in the winter form should also exist in nature. Indeed, it was soon discovered on the border of Iran and Turkey. Pumpkins and melons are characterized by simple and segmented fruits, but watermelon of this form was not described at the time of Vavilov. But segmented watermelons have been found in the southeast of the European part of Russia. The culture is dominated by the cultivation of three-sprout beets, the crops of which require weeding and removal of two extra shoots. But among the relatives of beets in nature there were also single-sprouted forms, so scientists were able to create a new variety of single-sprouted beets. Awnlessness of cereal crops is a mutation that has proven beneficial in the introduction of machine harvesting when the machinery is less clogged. Breeders, using the Vavilov law, found awnless forms and created new varieties of awnless cereals. The facts of parallel variability in close and distant species were already known to C. Darwin. For example, the same coat color of rodents, albinism in representatives different groups fauna and humans (a case of albinism in Negroes is described), lack of plumage in birds, lack of scales in fish, similar coloring of fruits of fruit and berry crops, variability of root crops, etc. The reason for the parallelism in variability lies in the fact that the basis of homologous characters lies the presence of similar genes: the genetically closer the species and genera, the more complete the similarity in the series of variability. Hence - the cause of homologous mutations - the common origin of genotypes. Nature in the process of evolution it was programmed, as it were, according to one formula, regardless of the time of origin of the species. The law of homological series in hereditary variability by NI Vavilov was not only a confirmation of Darwin's theory of the origin of species, but also expanded the concept of hereditary variability. Nikolai Ivanovich can again be proclaimed: “Thanks to Darwin!”, but also “Continuing Darwin!” Let's go back to 1920. The recollections of eyewitnesses are interesting. Alexandra Ivanovna Mordvinkina, who was present at the congress of the Saratov Agricultural Institute (later a candidate of biological sciences), recalled: “The congress opened in the largest auditorium of the university. Not a single report subsequently made such a strong impression on me as the speech of Nikolai Ivanovich. He spoke with inspiration, everyone listened with bated breath, it was felt that something very big and new in science was opening before us. When there was a stormy, long-lasting applause, Professor Vyacheslav Rafailovich Zelensky said: "These are biologists who greet their Mendeleev." The words of Nikolai Maksimovich Tulaikov especially imprinted in my memory: “What can be added to this report? I can say one thing: Russia will not perish if it has such sons as Nikolai Ivanovich. Nikolai Vladimirovich Timofeev-Resovsky, an excellent geneticist who knew Vavilov not only by work, but also personally, spoke confidentially to close acquaintances: “Nikolai Ivanovich was a wonderful person and great martyr, an excellent plant grower and gatherer, a traveler, a brave and universal favorite, but his series - the law is not at all homological, but analogous series, yes, sir! What is homology? This similarity is based on a common origin. What is an analogy? The similarity of external signs, which is determined by a similar habitat, but not by kinship. So who is right? Vavilov! One can only admire the depth of his biological mind! Changing just one term in the title also changes the essence of the law. According to the law of homologous series, all people are equal, because one biological origin, and belong to the homo sapiens species, that is, everyone is equally smart, capable and talented, etc., but they have external differences: in height, proportions between body parts, etc. According to the law of analogous series, people are outwardly similar, because they have a similar habitat, but a different origin. And this is already room for chauvinism, racism, nationalism, up to genocide. And the Vavilov law says that the pygmy of Africa and the basketball player of America are of the same genetic root, and one cannot be placed over the other - this is unscientific! The validity of the universal biological regularity discovered by Vavilov has been confirmed by modern research not only in plants, but also in animals. Modern genetics believe that the law reveals boundless prospects scientific knowledge, generalizations and foresight” (Professor M. E. Lobanov). Another fundamental work by N. I. Vavilov, “Plant Immunity to Infectious Diseases” (1919), belongs to the Saratov period. On the title page Book Nikolai Ivanovich wrote: "Dedicated to the memory of the great researcher of immunity Ilya Ilyich Mechnikov." No great scientist sees himself as a stand-alone in science. So Vavilov, thanks to Mechnikov, asked himself the question, can plants have protective forces if animals have them? In search of an answer to the question, he conducted research on cereals according to an original method and, summarizing practice and theory, laid the foundations of a new science - phytoimmunology. The work was purely practical value- use the natural immunity of plants as the most rational and cost-effective way to control pests. The young scientist created an original theory of the physiological immunity of plants to infectious diseases, and the study of genotypic immunity formed the basis of the doctrine. N. I. Vavilov studied the reaction of the "host" to the introduction of the parasite, the specificity of this reaction, and found out whether the entire series is immune, or only certain types of this series. Nikolai Ivanovich attached particular importance to group immunity, believing that in breeding it is important to develop varieties that are resistant not to one race, but to a whole population of physiological races, and such resistant species should be sought in the plant's homeland. Science later confirmed that wild species - relatives of cultivated plants - have natural immunity and are less susceptible to infectious diseases. It is the introduction of resistance genes into plants that modern breeders are engaged in, using the theory of N. I. Vavilov and genetic engineering methods. The scientist was interested in the development of immunity issues throughout his entire career. scientific activity: “The doctrine of plant immunity to infectious diseases” (1935), “The laws of natural plant immunity to infectious diseases (keys to finding immune forms)” (published only in 1961). Academician Petr Mikhailovich Zhukovsky rightly noted: “In the Saratov period, although it was short (1917-1921), the star of N. I. Vavilov, the scientist, rose.” Later, Vavilov would write: “I migrated from Saratov in March 1921 with the entire laboratory of 27 people.” He was elected head of the Bureau of Applied Botany of the Agricultural Scientific Committee in Petrograd. From 1921 to 1929 - Professor of the Department of Genetics and Breeding of the Leningrad Agricultural Institute. In 1921, V. I. Lenin sent two scientists to a conference in America, one of them - N. I. Vavilov. The report on genetic research made him popular among the scientists of the conference. In America, his performances were accompanied by a standing ovation, similar to the one that was later for Chkalov. “If all Russians are like that, then we need to be friends with them,” American newspapers shouted. In the 20-30s. N. I. Vavilov also manifests himself as a major organizer of science. He was actually the founder and permanent leader of the All-Union Institute of Plant Industry (VIR). In 1929, the All-Union Academy of Agricultural Sciences (VASKhNIL) was created on the basis of the All-Union Institute of Experimental Agronomy, which had previously been organized by Vavilov. He was elected the first president (from 1929 to 1935). With the direct participation of the scientist, the Institute of Genetics of the USSR Academy of Sciences was organized. In a short time, Vavilov's talent created scientific school geneticists, which has become the world's leading. All the initial work in our country in the field of genetics was carried out by him or under his direction. In VIR, the method of experimental polyploidy was first used, and G. D. Karpechenko began work on its use in distant hybridization. Vavilov insisted on starting work on the use of the phenomenon of heterosis and interline hybridization. Today it is the ABC of selection, but then it was the beginning. Over 30 years of scientific activity, about 400 works and articles have been published! Phenomenal memory, encyclopedic knowledge, knowledge of almost twenty languages, aware of all the innovations in science. He worked 18-20 hours a day. Mom scolded him: “You don’t even have time to sleep ...,” recalls Vavilov’s son.

Law of homologous series

The processing of extensive material of observations and experiments, a detailed study of the variability of numerous Linnaean species (Linneons), a huge amount of new facts obtained mainly from the study of cultivated plants and their wild relatives, allowed N.I. Vavilov to bring together all known examples of parallel variability and formulate a general law, which he called the "Law of homological series in hereditary variability" (1920), reported by him at the Third All-Russian Congress of Breeders, held in Saratov. In 1921 N.I. Vavilov was sent to America to attend the International Congress on Agriculture, where he delivered a report on the law of homologous series. The law of parallel variability of closely related genera and species, established by N.I. Vavilov and associated with a common origin, developing evolutionary doctrine Ch. Darwin, was duly appreciated by world science. It was perceived by the audience as the biggest event in the world biological science, which opens the widest horizons for practice.

The law of homological series, first of all, establishes the foundations of the taxonomy of the huge variety of plant forms that the organic world is so rich in, allows the breeder to get a clear idea of ​​​​the place of each, even the smallest, systematic unit in the plant world and judge the possible diversity of the source material for selection.

The main provisions of the law of homological series are as follows.

"one. Species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity that, knowing the number of forms within one species, one can foresee the occurrence of parallel forms in other species and genera. The closer genera and linneons are genetically located in the general system, the more complete is the similarity in the series of their variability.

2. Whole families of plants are generally characterized by a certain cycle of variability passing through all the genera and species that make up the family.

Even at the III All-Russian Congress on Selection (Saratov, June 1920), where N.I. Vavilov reported his discovery for the first time, all participants of the congress recognized that “like the periodic table (periodic system)” the law of homological series will allow predicting the existence, properties and structure of still unknown forms and species of plants and animals, and highly appreciated the scientific and practical significance of this law . Modern advances in molecular cell biology make it possible to understand the mechanism of the existence of homological variability in similar organisms - what exactly is the basis for the similarity of future forms and species with existing ones - and to meaningfully synthesize new forms of plants that are not found in nature. Now new content is being introduced into Vavilov's law, just like the appearance quantum theory gave a new deeper content to Mendeleev's periodic system.

The doctrine of the centers of origin of cultivated plants

By the mid-20s, the study of the geographical distribution and intraspecific diversity of various agricultural crops, carried out by N.I. Vavilov and under his leadership, allowed Nikolai Ivanovich to formulate ideas about the geographical centers of origin of cultivated plants. The book "Centers of Origin of Cultivated Plants" was published in 1926. The deeply theoretically substantiated idea of ​​centers of origin gave scientific basis for targeted searches for plants useful to humans, was widely used for practical purposes.

No less important for world science is the teaching of N.I. Vavilov about the centers of origin of cultivated plants and about geographical patterns in the distribution of their hereditary characteristics (first published in 1926 and 1927). In these classic works, N.I. Vavilov for the first time presented a harmonious picture of the concentration of a huge wealth of forms of cultivated plants in a few primary centers of their origin and approached the solution of the problem of the origin of cultivated plants in a completely new way. If before him botanists-geographers (Alphonse de Candol and others) searched "in general" for the homeland of wheat, then Vavilov searched for the centers of origin of individual species, groups of wheat species in various regions of the globe. At the same time, it was especially important to identify areas of natural distribution (ranges) of varieties of this species and to determine the center of the greatest diversity of its forms (botanical-geographical method).

To establish the geographical distribution of varieties and races of cultivated plants and their wild relatives, N.I. Vavilov studied the centers of the most ancient agricultural culture, the beginning of which he saw in the mountainous regions of Ethiopia, Western and Central Asia, China, India, in the Andes of South America, and not in the wide valleys of large rivers - the Nile, Ganges, Tigris and Euphrates, as scientists had previously claimed. . The results of subsequent archaeological research support this hypothesis.

To find the centers of diversity and richness of plant forms, N.I. Vavilov organized, according to a specific plan corresponding to his theoretical discoveries (homologous series and centers of origin of cultivated plants), numerous expeditions, which in 1922-1933. visited 60 countries of the world, as well as 140 regions of our country. As a result, a valuable fund of world plant resources has been collected, numbering over 250,000 samples. The collected richest collection was carefully studied using the methods of selection, genetics, chemistry, morphology, taxonomy and in geographical crops. It is still kept in VIR and is used by our and foreign breeders.

Creation of N.I. Vavilov modern teaching about selection

The systematic study of the world's plant resources of the most important cultivated plants has radically changed the idea of ​​the varietal and species composition of even such well-studied crops as wheat, rye, corn, cotton, peas, flax and potatoes. Among the species and many varieties of these cultivated plants brought from expeditions, almost half turned out to be new, not yet known to science. The discovery of new species and varieties of potatoes completely changed the previous idea of ​​the source material for its selection. Based on the material collected by the expeditions of N.I. Vavilov and his collaborators, the entire cotton breeding was based, and the development of the humid subtropics in the USSR was built.

Based on the results of a detailed and long-term study of varietal wealth collected by expeditions, differential maps of the geographical localization of varieties of wheat, oats, barley, rye, corn, millet, flax, peas, lentils, beans, beans, chickpeas, chinka, potatoes and other plants were compiled . On these maps it was possible to see where the main varietal diversity of these plants is concentrated, i.e., where the source material for the selection of a given crop should be drawn. Even for such ancient plants as wheat, barley, corn, and cotton, which have long settled throughout the globe, it was possible to establish with great accuracy the main areas of primary species potential. In addition, the coincidence of the areas of primary morphogenesis was established for many species and even genera. Geographical study led to the establishment of entire cultural independent floras specific to individual regions.

The study of world plant resources allowed N.I. Vavilov to fully master the source material for selection work in our country, and he reposed and solved the problem of source material for genetic and selection research. He developed the scientific foundations of breeding: the doctrine of the source material, the botanical and geographical basis of plant knowledge, breeding methods for economic traits involving hybridization, incubation, etc., the importance of distant interspecific and intergeneric hybridization. All these works have not lost their scientific and practical significance at the present time.

The botanical and geographical study of a large number of cultivated plants led to the intraspecific taxonomy of cultivated plants, as a result of which the works of N.I. Vavilov "Linnean species as a system" and "The doctrine of the origin of cultivated plants after Darwin".