An example of the operation of the law of homologous series of hereditary variability. Homologous series in hereditary variability law

N.I. Vavilov, studying hereditary variability in cultivated plants and their ancestors, discovered a number of patterns that made it possible to formulate the law of homologous series hereditary variability: “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 finding of parallel forms in other species and genera. The closer genera and species are genetically located in the general system, the more complete is the similarity in the series of their variability. Entire families of plants are generally characterized by a certain cycle of variability passing through all the genera and species that make up the 30 family.

This law can be illustrated by the example of the Bluegrass family, which includes wheat, rye, barley, oats, millet, etc. Thus, the black color of the caryopsis was found in rye, wheat, barley, corn and other plants, the elongated shape of the caryopsis was found in all the studied species of the family. The law of homological series in hereditary variability allowed N.I. Vavilov himself to find a number of previously unknown forms of rye, based on the presence of these characters in wheat. These include: awned and awnless ears, grains of red, white, black and purple color, mealy and vitreous grain, etc.

The law discovered by N.I. Vavilov is valid not only for plants, but also for animals. Thus, albinism occurs not only in different groups mammals, but also birds and other animals. Short-fingeredness is observed in humans, cattle, sheep, dogs, birds, lack of feathers in birds, scales in fish, wool in mammals, etc.

The law of homological series of hereditary variability is of great importance for breeding practice. It allows predicting the presence of forms not found in a given species, but characteristic of closely related species, that is, the law indicates the direction of the search. Moreover, the desired form can be found in the wild or obtained by artificial mutagenesis. For example, in 1927, the German geneticist E. Baur, based on the law of homologous series, suggested the possible existence of an alkaloid-free form of lupine that could be used for animal feed. However, such forms were not known. It has been suggested that non-alkaloid mutants are less resistant to pests than bitter lupine plants, and most of them die before flowering.

Based on these assumptions, R. Zengbush began the search for alkaloid-free mutants. He examined 2.5 million lupine plants and identified among them 5 plants with a low content of alkaloids, which were the ancestors of fodder lupine.

Later studies showed the effect of the law of homological series on the level of variability of morphological, physiological and biochemical characteristics of a wide variety of organisms - from bacteria to humans.

Artificial obtaining of mutations

In nature, spontaneous mutagenesis is constantly going on. However, spontaneous mutations are rare. For example, in Drosophila, the white eye mutation occurs at a rate of 1:100,000 gametes; in humans, many genes mutate at a rate of 1:200,000 gametes.

In 1925, G.A. Nadson and G.S. Filippov discovered the mutagenic effect of radium rays on hereditary variability in yeast cells. Of particular importance for the development of artificial mutagenesis were the works of G. Meller (1927), who not only confirmed the mutagenic effect of radium rays in experiments on Drosophila, but also showed that irradiation increases the frequency of mutations hundreds of times. In 1928, L. Stadler used X-rays to obtain mutations. Later, the mutagenic effect of chemicals was also proven. These and other experiments have shown the existence of a large number of factors called mutagenic capable of causing mutations in various organisms.

All mutagens used to obtain mutations are divided into two groups:

physical - radiation, high and low temperature, mechanical impact, ultrasound;

chemical- various organic and inorganic compounds: caffeine, mustard gas, heavy metal salts, nitrous acid, etc.

Induced mutagenesis is of great importance. It makes it possible to create a valuable source material for breeding, hundreds of highly productive varieties of plants and animal breeds, increase the productivity of a number of producers of biologically active substances by 10-20 times, and also reveals ways to create means of protecting humans from the action of mutagenic factors.

The study of hereditary variability in various systematic groups plants allowed N. I. Vavilov to formulate law of homologous series.

This law says:

"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 (species) 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.

N. I. Vavilov expressed his law by the formula:

G 1 (a + b + c + ... +),

G 2 (a + b + c + ... +),

G 3 (a + b + c + ... +),

where G 1, G 2, G 3 denote species and a, b, c ... - various varying features, such as color, shape of stems, leaves, seeds, etc.

An illustration of the law can be a table that shows the homology of hereditary variability in certain traits and properties within the family of cereals. But this list of features and properties could be significantly expanded.

At present, it can be said with good reason that similar mutations arise in related species that have a common origin. Moreover, even among representatives of different classes and types of animals, we encounter parallelism - homologous series of mutations according to morphological, physiological, and especially biochemical characteristics and properties. So, for example, similar mutations are found in different classes of vertebrates: albinism and hairlessness in mammals, albinism and lack of feathers in birds, lack of scales in fish, short-fingeredness in cattle, sheep, dogs, birds, etc.

Homologous series of mutational variability of biochemical traits are found not only in higher organisms, but also in protozoa and microorganisms. The data on biochemical mutants, which can be interpreted as a homologous series, are given. The table shows data on biochemical mutants that can be interpreted as a homologous series.

As we can see, the accumulation of similar substances (tryptophan or kynurenine), determined by genes, occurs in very different groups of animals: Diptera, Hymenoptera, and butterflies. In this case, the biosynthesis of pigments is achieved in a similar way.

Based on the law of homological series, it should be assumed that if a series of spontaneous or induced mutations is found in one species of animal or plant, then a similar series of mutations can be expected in other species of this genus. The same applies to higher systematic categories. The reason for this is the common origin of genotypes.

The most probable explanation for the origin of the homologous series of hereditary variability is as follows. Related species within the same genus, genera within the same order or family, could arise through the selection of various beneficial mutations of individual common genes, the selection of forms with various beneficial chromosomal rearrangements. In this case, related species that diverged in evolution due to the selection of different chromosomal rearrangements could carry homologous genes, both original and mutated. Species could also arise by selecting spontaneous polyploids containing homogeneous sets of chromosomes. The divergence of species based on these three types of hereditary variability ensures the commonality of genetic material in related systematic groups. But in reality the situation is, of course, more complicated than it seems to us now.

Perhaps biochemical studies of chromosomes, the study of their structure and the role of DNA as a material carrier hereditary information lift the veil over this still unknown phenomenon of homology and analogy of the ways of development of organic forms.

If nucleic acids in a complex with a protein are the primary substrate that provided the programming of the evolution of living systems from the earliest stages, then the law of homological series acquires universal significance as the law of the emergence of similar series of biological mechanisms and processes occurring in organic nature. This applies both to the morphology of tissues, their functional properties, biochemical processes, adaptation mechanisms etc., and to the genetic mechanisms of all living organisms. The analogy is observed for all major genetic phenomena:

• cell division,
• mechanism of mitosis
• mechanism of chromosome reproduction,
• mechanism of meiosis
• fertilization,
• recombination mechanism,
• mutations, etc.

Living nature in the process of evolution was, as it were, programmed according to one formula, regardless of the time of origin of one or another type of organisms. Of course, such hypothetical considerations require confirmation on the basis of a synthesis of many knowledge, but it is obvious that the solution of this fascinating problem is the work of the current century. It should force researchers to look not so much for particular differences that characterize the divergence of species as for their common features, which are based on similar genetic mechanisms.

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When comparing the characteristics of various varieties of cultivated plants and wild species close to them, M. I. Vavilov discovered many common hereditary changes. This allowed him to formulate in 1920 law of homologous series in hereditary variability: genetically close species and genera are characterized by similar series of hereditary variability with such regularity that, having studied a number of forms within the same species or genus, one can assume the presence of forms with similar combinations of characters within related species or genera.

Examples illustrating this pattern are: in wheat, barley and oats there are white, red and black colors of the ear; in cereals, forms with long and short awns are known, etc. M. I. Vavilov pointed out that homologous series often go beyond genera and even families. Short-fingeredness has been noted in representatives of many mammalian ranks: in cattle, sheep, dogs, and humans. Albinism is observed in all classes of vertebrates.

The law of homological series makes it possible to foresee the possibility of the appearance of mutations still unknown to science, which can be used in breeding to create new forms valuable for the economy. In 1920, when the law of homologous series was formulated, the winter form of durum wheat was not yet known, but its existence was foreseen. A few years later, such a form was discovered in Turkmenistan. In cereals (wheat, barley, oats, corn) there are naked and filmy grains. The naked variety of millet was not known, but the existence of such a form was to be expected, and it was found. Homological series are based on phenotypic similarity, which arises as a result of the action of the same alleles of the same gene, as well as the action of different genes that cause similar chains of successive biochemical reactions in the body.

The law of homological series provides the key to understanding the evolution of related groups, facilitates the search for hereditary deviations for selection, and in taxonomy makes it possible to find new expected forms. The law directly concerns the study of human hereditary diseases. The issues of treatment and prevention of hereditary diseases cannot be solved without research on animals with hereditary anomalies similar to those observed in humans. According to the law M. I. Vavilov, phenotypes similar to human hereditary diseases are also found in animals. Indeed, many of the pathological conditions identified in animals may be models of human hereditary diseases. So, dogs have hemophilia, which is sex-linked. Albinism has been reported in many species of rodents, cats, dogs, and a number of birds. To study muscular dystrophy, mice, cattle, horses are used, epilepsy - rabbits, rats, mice. Hereditary deafness exists in guinea pigs, mice and dogs. Deficiencies in the structure of the human face, homologous to the "cleft lip" and "cleft palate", are observed in the facial region of the skull of mice, dogs, pigs. Mice suffer from hereditary metabolic diseases, such as obesity and diabetes mellitus. In addition to already known mutations, exposure to mutagenic factors can get many new anomalies in laboratory animals, similar to those found in humans.

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 characteristics 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 the better studied cereals with a huge number of already known, studied varieties and forms, several hundred different characters are described, while other, less studied or wild relatives of cultivated species do not have many features, 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 fundamentals further selection and search for economically useful traits in plants introduced into the culture. The study of homologous series of hereditary variability, first of all in cultivated plants, then in domestic animals, is now taken for granted, 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 marked everything on large-scale maps with colored pencils, at first playing, like little children, at geographic Maps, and then translating all this into relatively simple small cards with black icons of various types for different forms 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, well, let's say, in Northern or Central China or in a mountainous part 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 places. 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 in the first place. and in the areas occupied by deserts and wastelands, combined with the protection of nature 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.

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 for the International Congress on agriculture, where he made a presentation 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 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 value 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 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.