What law formulated N and Vavilov. Law of homologous series of hereditary variability

The law, which was discovered by the outstanding Russian scientist N. I. Vavilov, is the most powerful stimulator for the selection of new plant and animal species that are beneficial to humans. Even at the present time, this regularity plays an important role in the study of evolutionary processes and the development of an acclimatization base. The results of Vavilov's research are also important for the interpretation of various biogeographic phenomena.

The Essence of the Law

Briefly, the law of homological series is as follows: the spectra of variability in related types of plants are similar to each other (often this is a strictly fixed number of certain variations). Vavilov presented his ideas at the III Selection Congress, which was held in 1920 in Saratov. To demonstrate the operation of the law of homologous series, he collected the entire set of hereditary characteristics of cultivated plants, arranged them in one table and compared the varieties and subspecies known at that time.

plant study

Along with cereals, Vavilov also considered legumes. In many cases parallelism was found. Despite the fact that each family had different phenotypic characteristics, they had their own characteristics, form of expression. For example, the color of the seeds of almost any cultivated plant ranged from the lightest to black. In cultivated plants well studied by researchers, up to several hundred traits were found. In others, which were at that time less studied or wild relatives of cultivated plants, much less signs were observed.

Geographic centers of species distribution

The basis for the discovery of the law of homological series was the material that Vavilov collected during his expedition to the countries of Africa, Asia, Europe and America. The first assumption that there are certain geographical centers from which biological species originate was made by the Swiss scientist A. Decandol. According to his ideas, once these species covered large territories, sometimes entire continents. However, it was Vavilov who was the researcher who was able to study the diversity of plants on a scientific basis. He used a method called differential. The entire collection that was collected by the researcher during the expeditions was subjected to a thorough analysis using morphological and genetic methods. So it was possible to determine the final area of concentration of the diversity of forms and features.

plant map

During these trips, the scientist did not get confused in the variety of different plant species. He put all the information with colored pencils on maps, then translating the material into a schematic form. Thus, he was able to discover that on the entire planet there are only a few centers of diversity of cultivated plants. The scientist showed directly with the help of maps how species "spread" from these centers to other geographical regions. Some of them go a short distance. Others conquer the whole world, as happened with wheat and peas.

Consequences

According to the law of homological variability, all genetically close plant varieties have approximately equal series of hereditary variability. At the same time, the scientist admitted that even outwardly similar signs may have a different hereditary basis. Given the fact that each of the genes has the ability to mutate in different directions and that this process can proceed without a specific direction, Vavilov made the assumption that the number of gene mutations in related species will be approximately the same. The law of homological series by N. I. Vavilov reflects the general patterns of gene mutation processes, as well as the formation of various organisms. It is the main basis for the study of biological species.

Vavilov also showed the corollary that followed from the law of homologous series. It sounds like this: hereditary variability in almost all plant species varies in parallel. The closer the species are to each other, the more this homology of characters manifests itself. Now this law is universally applied in the selection of agricultural crops, as well as animals. The discovery of the law of homologous series is one of the greatest achievements of the scientist, which brought him worldwide fame.

Plant origin

The scientist created a theory about the origin of cultivated plants in remote points of the globe in various prehistoric eras. According to Vavilov's law of homologous series, related plant and animal species exhibit similar variations in trait variability. The role of this law in crop and animal husbandry can be compared with the role played by D. Mendeleev's table of periodic elements in chemistry. Using his discovery, Vavilov came to the conclusion about which territories are the primary sources of certain types of plants.

The world owes the origin of rice, millet, naked forms of oats, and many types of apple trees to the Sino-Japanese region. Also, the territories of this region are home to valuable varieties of plums, oriental persimmons.
coconut palm and sugarcane - Indonesian-Indochinese center.
With the help of the law of homological series of variability, Vavilov managed to prove the great importance of the Hindustan Peninsula in the development of crop production. These territories are home to some types of beans, eggplants, cucumbers.
On the territory of the Central Asian region, walnuts, almonds, pistachios were traditionally grown. Vavilov discovered that this territory is the birthplace of onions, as well as the primary types of carrots. In ancient times, apricots were grown. One of the best in the world are melons, which were bred in the territories of Central Asia.
Grapes first appeared in the Mediterranean territories. The process of evolution of wheat, flax, various varieties of oats also took place here. Also fairly typical elements of the Mediterranean flora is the olive tree. The cultivation of lupine, clover and flax also began here.
Flora of the Australian continent gave the world eucalyptus, acacia, cotton.
The African region is the birthplace of all types of watermelons.
In the European-Siberian territories, sugar beets, Siberian apple trees, and forest grapes were cultivated.
South America is the birthplace of cotton. The Andes territory is also home to some types of tomatoes. In the territories of ancient Mexico, corn and some types of beans grew. Tobacco also originated here.
In the territories of Africa, ancient man used at first only local plant species. The black continent is the birthplace of coffee. Wheat first appeared in Ethiopia.

Using the law of homological series of variability, a scientist can identify the center of origin of plants by those features that are similar to the forms of species from another geographical area. In addition to the necessary variety of flora, in order to develop a large center of diverse cultivated plants, an agricultural civilization is also needed. So thought N. I. Vavilov.

domestication of animals

Thanks to the discovery of the law of homologous series of hereditary variability, it became possible to discover those places where the domestication of animals once took place for the first time. It is believed that it happened in three ways. This is the rapprochement of man and animals; forcible domestication of young individuals; domestication of adults. The territories where the domestication of wild animals took place are presumably located in the habitats of their wild relatives.

Taming in different eras

It is believed that the dog was domesticated during the Mesolithic era. Man began to breed pigs and goats in the Neolithic era, and a little later wild horses were tamed. However, the question of who the ancestors of modern domestic animals were is still not clear enough. It is believed that the ancestors of cattle were tours, horses - tarpans and Przhevalsky horses, domestic goose - wild gray goose. Now the process of domestication of animals cannot be called complete. For example, arctic foxes and wild foxes are in the process of taming.

Significance of the law of homologous series

With the help of this law, one can not only establish the origin of certain plant species and the centers of domestication of animals. It allows you to predict the appearance of mutations by comparing patterns of mutation in other types. Also, using this law, it is possible to predict the variability of a trait, the possibility of the appearance of new mutations by analogy with those genetic abnormalities that were found in other species related to this plant.

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 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 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 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 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 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".

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, which differ in shape, depending on the action of the 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, to a greater extent, 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 spikelets 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) .

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.

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.

AT) 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. The reasons: 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 an individual of a population carries, 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, and form 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.