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N Vavilov discovered the law of homological series. The law of homological series of hereditary variability of organisms

N Vavilov discovered the law of homological series. The law of homological series of hereditary variability of organisms

Sections: Biology

Lesson objectives

Introduce students to forms hereditary variability, their causes and effects on the body. To develop in schoolchildren the ability to classify the forms of variability, to compare them with each other; give examples illustrating the manifestation of each of them;
To form knowledge about the types of mutations;
Formulate the law of homologous series and explain its meaning;
Convince high school students that the mutation process is very important for the evolution of the organic world and human selection work.

Demonstrations

Scheme of different types of chromosomal mutations.
Scheme of polyploidization.
Homological series in hereditary variability.

Terms Genotypic variability, mutation, gene mutations, genomic mutations, chromosomal mutations:

inversion;
deletion;
duplication;
translocation.

Tasks for students:

Formulate the law of homologous series and give examples.
Get acquainted with the biography of N.I. Vavilov and know his main scientific discoveries.
Make a table "Forms of variability"

Organizing time.

Testing knowledge and skills.

Front work

What does genetics study?
What does the term heredity mean? - variability?
What forms of variability do you know?
What does reaction rate mean?
What are the patterns of modification variability?
How does changing conditions affect quantitative and qualitative traits? Give examples
What is a reaction rate? Why is the variety of qualitative features in small degree does it depend on environmental conditions?
What is the practical significance in agriculture of the value of the reaction rate of animals and plants?

Individual work on the computer - test work

Fill in the chart:

Work of students on computers with the application 1 . (During the lesson, tasks 1-5 are completed).

Learning new material

The concept of hereditary variability includes genotypic and cytoplasmic variability. The first is divided into mutational, combinative, correlative. Combination variation occurs with crossing over, independent divergence of chromosomes in meiosis, and random fusion of gametes during sexual reproduction. The composition of mutational variability includes genomic, chromosomal and gene mutations. The term mutation was introduced into science by G. de Vries. His biography and main scientific achievements located in the section. Genomic mutations are associated with the occurrence of polyploids and aneuploids. Chromosomal mutations are determined by interchromosomal changes - translocation or intrachromosomal rearrangements: deletion, duplication, inversion. Gene mutations are explained by changes in the sequence of nucleotides: an increase or decrease in their number (deletion, duplication), insertion of a new nucleotide, or rotation of a section within a gene (inversion). Cytoplasmic variability is associated with DNA, which is found in the plastids and mitochondria of the cell. The hereditary variability of related species and genera obeys the law of Vavilov's homologous series.

Modification variability reflects changes in the phenotype without affecting the genotype. Opposite to it is another form of variability - genotypic, or mutational (according to Darwin - hereditary, indefinite, individual), changing the genotype. Mutation is a persistent hereditary change in genetic material.

Individual changes in the genotype are called mutations.

The concept of mutations was introduced into science by the Dutchman de Vries. Mutations are hereditary changes that lead to an increase or decrease in the amount of genetic material, to a change in nucleotides or their sequence.

Mutation classification

Mutations by the nature of manifestation: Dominant, recessive.
Mutations at the place of their occurrence: somatic, generative.
Mutations by the nature of appearance: spontaneous, induced.
Mutations by adaptive value: beneficial, harmful, neutral. (Lethal, semi-lethal.)

Most of the resulting mutations are recessive and unfavorable for the organism, they can even cause its death. In combination with an allelic dominant gene, recessive mutations do not appear phenotypically. Mutations occur in sex and somatic cells. If mutations occur in germ cells, they are called generative and manifest themselves in the generation that develops from germ cells. Changes in vegetative cells are called somatic mutations. Such mutations lead to a change in the trait of only a part of the organism that develops from the changed cells. In animals, somatic mutations are not transmitted to subsequent generations, since a new organism does not arise from somatic cells. It is different in plants: in hybrid cells of plant organisms, replication and mitosis can be carried out in different nuclei somewhat differently. Over the course of a number of cell generations, individual chromosomes are lost and certain karyotypes are selected that can be preserved for many generations.

There are several types of mutations according to the level of occurrence:

Genomic mutations - change in ploidy, i.e. chromosome numbers (numerical chromosome aberrations), which are especially common in plants;
Chromosomal mutations - changes in the structure of chromosomes (structural chromosomal aberrations);
Gene mutations - changes in individual genes;

Genomic mutations

Polyploidy is a multiple increase in the number of chromosomes.
Aneuploidy is the loss or appearance of extra chromosomes as a result of a violation of meiosis.

Occur due to a change in the number or structure of chromosomes. Changes in ploidy are observed in disorders of chromosome divergence.

Chromosomal diseases

generative mutations
XXY; HUU - Klinefelter's syndrome.
XO - Shershevsky-Turner syndrome.

Autosomal mutations

Patau syndrome (on chromosome 13).
Edwards syndrome (on chromosome 18).
Down syndrome (on chromosome 21).

Klinefelter syndrome.

XXY and XXXY - Klinefelter's syndrome. The frequency of occurrence is 1:400 - 1:500. The karyotype is 47, XXY, 48, XXXY, etc. The phenotype is male. Female body type, gynecomastia. Tall, relatively long arms and legs. Weakly developed hairline. Intelligence is reduced.

Shershevsky-Turner syndrome

X0 - Shereshevsky-Turner syndrome (monosomy X). The frequency of occurrence is 1:2000 - 1:3000. Karyotype 45,X. The phenotype is female. Somatic signs: height 135 - 145 cm, pterygoid skin fold on the neck (from the back of the head to the shoulder), low position of the ears, underdevelopment of primary and secondary sexual characteristics. In 25% of cases, there are heart defects and anomalies in the functioning of the kidneys. The intellect rarely suffers.

Patau syndrome - Trisomy on the 13th chromosome (Patau syndrome) is found in newborns with a frequency of about 1:5000 - 1:7000 and is associated with a wide range of malformations. SP is characterized by multiple congenital malformations of the brain and face. This is a group of early disorders in the formation of the brain, eyeballs, bones of the brain and facial parts of the skull. The circumference of the skull is usually reduced. Forehead sloping, low; the palpebral fissures are narrow, the nose bridge is sunken, the auricles are low and deformed. A typical sign of SP is cleft lip and palate.

Down Syndrome - A disease caused by an anomaly of the chromosome set (a change in the number or structure of autosomes), the main manifestations of which are mental retardation, a peculiar appearance of the patient and congenital malformations. One of the most common chromosomal diseases, occurs on average with a frequency of 1 in 700 newborns. A transverse fold is often found on the palm

Chromosomal mutations

There are several types of chromosomal mutations associated with changes in the structure of chromosomes:

deletion - loss of a portion of a chromosome;
duplication - doubling of a section of a chromosome;
inversion - rotation of a chromosome segment by 180 degrees;
translocation - the transfer of a section of a chromosome to another chromosome.
transposition - movement in one chromosome.

Deletions and duplications change the amount of genetic material. Phenotypically, they appear depending on how large the corresponding sections of chromosomes are and whether they contain important genes. Duplications can lead to the creation of new genes. During inversions and translocations, the amount of genetic material does not change, but its location changes. Such mutations also play an important role, since the crossing of mutants with the original forms is difficult, and their F1 hybrids are most often sterile.

Deletions. In humans, as a result of a deletion:

Wolf's syndrome - a lost section of the large chromosome 4 -
syndrome "cat's cry" - with a deletion in chromosome 5. Cause: chromosomal mutation; loss of a chromosome fragment in the 5th pair.
Manifestation: abnormal development of the larynx, feline-like screams, I in early childhood, lag in physical and mental development

Inversions

This is a change in the structure of the chromosome, caused by a 180 ° turn of one of its internal sections.
Similar chromosomal rearrangement is a consequence of two simultaneous breaks in one chromosome.

Translocations

During translocation, regions of nonhomologous chromosomes are exchanged, but the total number of genes does not change.

Base replacement

phenylketonuria. Manifestation: impaired cleavage of phenylalanine; this is due to dementia caused by hyperphenylalaninemia. With a timely prescribed and observed diet (nutrition, low phenylalanine) and the use of certain medications, clinical manifestations this disease is almost non-existent.
sickle cell anemia.
Morfan syndrome.

Genetic(point) mutations are associated with changes in the nucleotide sequence. The normal gene (peculiar to the wild type) and the mutant genes that arise from it are called alleles.

With gene mutations, the following structural changes occur:

gene mutation

For example, sickle cell anemia is the result of a single base substitution in the b-chain of blood globin (adenine is replaced by thymine). During deletion and duplication, the sequence of triplets is shifted and mutants with a “frameshift” appear, i.e. shifts of boundaries between codons - all subsequent amino acids change from the place of mutation.

The primary structure of hemoglobin in healthy (1) and patients with sickle cell anemia (2).

- val-gis-ley-tre - pro-glut. to-ta- glu-liz
- val-gis-ley-tre - valine- glu-liz

Mutation in the beta hemoglobin gene

Morfan's syndrome

The high release of adrenaline, characteristic of the disease, contributes not only to the development of cardiovascular complications, but also to the appearance in some individuals of special fortitude and mental endowment. Methods of treatment are unknown. It is believed that Paganini, Andersen, Chukovsky were sick with it

Hemophilia

Mutagens are factors that cause mutations: biological, chemical, physical.

Experimentally, the mutation rate can be increased. Under natural conditions, mutations occur with sudden changes in temperature, under the influence of ultraviolet radiation, and for other reasons. However, in most cases, the true causes of mutations remain unknown. Currently, methods have been developed to increase the number of mutations by artificial means. For the first time, a sharp increase in the number of hereditary changes that occur was obtained under the influence of X-rays.

Physical factors (various types of ionizing radiation, ultraviolet radiation, X-rays)
Chemical factors (insecticides, herbicides, lead, drugs, alcohol, certain drugs and other substances)
Biological factors (viruses of smallpox, chickenpox, mumps, influenza, measles, hepatitis, etc.)

Eugenics.

Eugenics is the science of improving the breed of mankind.

Eugenics in Greek means the birth of the best. This scandalous science is looking for ways to improve the hereditary qualities of a person using genetic principles. It has always been difficult for it to remain a pure science: its development was closely followed by politics, which disposed of its fruits in its own way.

In ancient Sparta, the selection of people was carried out more radically, destroying babies who did not have the physical qualities necessary for a future warrior. The father of eugenics, which put it on a scientific basis, was Francis Galton in 1869. After analyzing the pedigrees of hundreds of talented people, he came to the conclusion that genius abilities are inherited.

Today, eugenics aims to eradicate hereditary diseases in the human race. Any biological species will be on the verge of destruction if its existence conflicts with nature. Almost half of newborns out of a thousand are born with some kind of hereditary pathology. In the world, 2 million such children are born every year. Among them - 150 thousand with Down syndrome. It has long been known to everyone that it is easier to prevent the birth of a child than to deal with ailments. But such opportunities have appeared only in our time. Prenatal diagnosis and genetic counseling help to solve the problem of the advisability of childbirth.

Modern possibilities of medical genetic counseling make it possible to determine the risk of hereditary diseases during pregnancy planning.

Nikolay Ivanovich Vavilov

Nikolai Ivanovich Vavilov (1887-1943) - Russian botanist, geneticist, plant grower, geographer. Formulated the law of homologous series of hereditary variability. Created the doctrine of centers of origin cultivated plants.

The Russian scientist N. I. Vavilov established an important pattern known as the law of homological series in hereditary variability: species and genera that are genetically close (related to each other by a unity of origin) are characterized by similar series in hereditary variability. On the basis of this law, one can foresee the discovery of similar changes in related species and genera. He compiled a table of homologous series in the family

cereals. In animals, this pattern also manifests itself: for example, in rodents there are homologous series in terms of coat color.

Law of homologous series

Studying the hereditary variability of cultivated plants and their ancestors, N.I. Vavilov formulated the law of homological series: “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, one can foresee the presence of parallel forms in other species and genera.”

Using the family of cereals as an example, Vavilov showed that similar mutations are found in a number of species of this family. So, the black color of seeds is found in rye, wheat, barley, corn and others, with the exception of oats, wheatgrass, and millet. The elongated shape of the grain is found in all studied species. Animals also have similar mutations: albinism and lack of hair in mammals, short-fingeredness in cattle, sheep, dogs, birds. The reason for the appearance of similar mutations is the common origin of genotypes.

Thus, the detection of mutations in one species provides a basis for searching for similar mutations in related plant and animal species.

Law of homologous series

What mutant forms should arise in closely related species?
Who is the founder of the law of homologous series?
How does the law say?

Homework.

Section 24
Find examples of mutations in nature.

homologous series). Formulated in 1920 by N. I. Vavilov, who discovered that the hereditary variability of plants is similar in closely related species and genera of the grass family. It manifests itself in a change in similar characters with such regularity that, knowing the forms of plants in representatives of one species, one can foresee the appearance of these forms in other related species and genera. The closer the species are to each other by origin, the more clearly this similarity is manifested. Yes, at various kinds In wheat (for example, soft and durum), series of similar hereditary changes are revealed in the awn of the ear (awned, semi-awned, awnless), its color (white, red, black, gray ears), the shape and texture of the grain, early maturity, cold resistance, responsiveness to fertilizers, and so on.

Similar variability in the awning of the ear in soft wheat (1-4), durum wheat (5-8) and six-row barley (9-12) (according to N. I. Vavilov).

The parallelism of variability is more weakly expressed in different genera within the family (for example, wheat, barley, rye, oats, couch grass and other genera from the family of cereals) and even weaker in different families within the order (higher taxonomic rank). In other words, in accordance with the law of homology series, closely related species due to the great similarity of their genomes (almost identical sets of genes) have similar potential variability of traits, which is based on similar mutations of homologous (orthologous) genes.

N. I. Vavilov pointed out the applicability of homological series of laws to animals as well. Obviously, this is a universal law of variability, covering all the kingdoms of living organisms. The validity of this law is vividly illustrated by genomics, which reveals the similarity of the primary structure of the DNA of closely related species. The law of homology series finds further development in the modular (block) principle of the theory of molecular evolution, according to which the genetic material diverges through duplications and subsequent combinatorics of DNA sections (modules).

The law of homology series helps to purposefully search for hereditary changes necessary for selection. It indicates to breeders the direction of artificial selection, facilitates the production of forms that are promising for the selection of plants, animals and microorganisms. For example, guided by the law of homology series, scientists have created alkaloid-free (non-bitter) varieties of fodder lupins for pasture animals, while enriching the soil with nitrogen. The law of homology series also helps to navigate in the choice of model objects and specific genetic systems (genes and traits) for modeling and searching for therapy for human hereditary diseases, such as metabolic diseases, neurodegenerative diseases, etc.

Lit .: Vavilov N. I. The law of homological series in hereditary variability. M., 1987.

S. G. Inge-Vechtomov.

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 all known examples of parallel variability into a single whole and formulate common law, called by him "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 the evolutionary teachings of Charles Darwin, was duly appreciated by world science. It was perceived by the audience as the largest event in the world biological science, which opens up 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.

"1. 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 table)” 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 - on what exactly the similarity of future forms and species with existing ones is based - 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 new deeper content periodic system Mendeleev.

In 1920 N.I. Vavilov presents the main ideas of the Law of Homological Series in a report at the III All-Russian Breeding Congress in Saratov. Main idea: related plant species have similar spectra of variability (often a fixed number of well-defined variations).

“And Vavilov did such a thing. He collected all known hereditary traits from the best studied, as I have already said, plants from among cultivated cereals, arranged them in a certain order in tables and compared all subspecies, forms and varieties known to him at that time. There were many tables compiled, of course, the material was huge. At the same time, back in Saratov, he fastened legumes to cereals - various peas, vetch, beans, beans, etc. - and some other crops. And it turned out in very many cases parallelism in very many species. Of course, for each family, genus, and species of plants, all signs had their own characteristics, their own form, their own way of expression. For example, seed color from almost white to almost black varied in almost all cultivated plants. This means that if in better studied cereals with a huge number of already known, studied varieties and forms, several hundred various signs, and other, less studied or wild relatives of cultivated species do not have many signs, then they can, so to speak, be predicted. They will still be found on the corresponding large material.

Vavilov showed that, on the whole, the hereditary variability of all plants varies in parallel to a very strong degree. He called it the homologous series of plant variability. And he pointed out that the closer the species are to each other, the greater this homology of the series of variability of characters. A number of different general regularities have been revealed in these homologous series of plant hereditary variability. And this circumstance was taken by Vavilov as one of the most important foundations for further selection and the 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 a matter of course, one of the foundations of further selection. necessary to a person varieties of certain species of plants under study. This was, perhaps, one of the first major achievements of Vavilov on a world scale, which very quickly created him a world name. The name, if not the first and best, then one of the first and best applied botanists in the world.

In parallel with this, Vavilov made all over the world - throughout Europe, most of Asia, a large part of Africa, North, Central and South America- a large number of expeditions with the collection of huge material, mainly on cultivated plants. In 1920, I think, Vavilov was made director of the Bureau of Applied Botany and New Cultures. This Bureau was somewhat changed and turned into the Institute for Applied Botany and New Crops, then the Institute for Applied Botany, Genetics and Plant Breeding. And by the end of the 1930s, it had already become the All-Union Institute of Plant Growing. This name has been preserved to this day, although its global share, of course, fell sharply 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 Tsarskoye 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 a huge amount of material, in this case already the geographical diversity of forms of various types of cultivated plants. He plotted everything on large-scale maps with multi-colored pencils, first playing, like small children, with geographical maps, and then translating all this into relatively simple small maps with black icons of various types for various forms of cultivated plants. So he discovered in the world, on the globe, in the biosphere of our planet, several centers of diversity of cultivated plants. And he showed, simply on maps, the spread, distribution on Earth not only of individual species, but of certain groups of species, cultivated, apparently, for the first time in a certain place, let's 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 one species of any cultivated plants, but a group of economically connected species that arose as cultivated plants and took root as cultivated plants in a certain place, spread over 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 the centers of diversity and origin of various forms of cultivated plants in different parts of the globe. And he created a whole theory of the origin of cultivated plants in various eras of the most ancient and ancient world. This was Vavilov's second great achievement, again world-class. 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, of some reform and modification of Vavilov's views, but we can say that these are particulars in comparison with the general world picture created by Vavilov.

This means that I have already listed three great achievements: plant immunity, the law of homological series, and the theory of centers of agriculture and the emergence of various forms of cultivated plants. Perhaps the last thing I would like to name from Vavilov’s overall achievements is a large number of his works and efforts, mainly efforts, already in the sense of propaganda at various congresses, international and all-Union, writing popular science articles on the problem of advancing agriculture to the north, primarily in areas occupied by deserts and wastelands, combined with nature protection in a completely modern and even intended for the near future sense: the promotion of culture along 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.

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 the evolutionary teachings of Charles Darwin, was duly appreciated by world science. It was perceived by the audience as the largest event in the world biological science, which opens up the widest horizons for practice.

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

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 table)” 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 - on what exactly the similarity of future forms and species with existing ones is based - and to meaningfully synthesize new forms of plants that are not found in nature. Now a new content is being introduced into Vavilov's law, just as the advent of quantum theory has given 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 provided a scientific basis for targeted searches for plants useful to humans, and 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 coherent picture of the concentration of an enormous 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 certain 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 of the modern doctrine of 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 been 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.

Botanical and geographical study a large number 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".