N.I. Vavilov, studying hereditary variability in cultivated plants and their ancestors, discovered a number of patterns that made it possible to formulate the law of homological series of hereditary variability: “Species and genera that are genetically close are characterized by similar series of hereditary variability with such correctness that, knowing a number of forms within one species, one can foresee the finding of parallel forms in other species and genera. The closer they are genetically located in common system genera and species, the more complete the similarity in the ranks of their variability. Whole families of plants are generally characterized by a certain cycle of variation passing through all the genera and species that make up the family 30.”

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

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

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

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

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

Artificial mutations

Spontaneous mutagenesis occurs constantly in nature. However, spontaneous mutations are rare. For example, in Drosophila, the white eye mutation is formed with a frequency of 1:100,000 gametes; in humans, many genes mutate with a frequency of 1:200,000 gametes.

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

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

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

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

Induced mutagenesis is of great importance. It makes it possible to create valuable source material for breeding, hundreds of highly productive plant varieties and animal breeds, and increase the productivity of a number of biological producers by 10-20 times. active substances, 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 of plants allowed N.I. Vavilov to formulate law of homological series.

This law states:

"1. Species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity that, knowing the series of forms within one species, one can predict the presence of parallel forms in other species and genera. The closer the genera and linneons (species) are genetically located in the general system, the more complete 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 with 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... are various varying characteristics, for example color, shape of stems, leaves, seeds, etc.

An illustration of the law can be a table that shows the homology of hereditary variability for some traits and properties within the cereal family. But this list of signs and properties could be significantly expanded.

At present, we can rightfully say that similar mutations occur 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 in morphological, physiological and especially biochemical characters and properties. So, for example, similar mutations occur in different classes of vertebrate animals: albinism and hairlessness in mammals, albinism and the absence of feathers in birds, absence of scales in fish, short-fingered feet in cattle, sheep, dogs, birds, etc.

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

As we 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 accepted that if a number of spontaneous or induced mutations are 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 the genotypes.

The most likely explanation of the origin of homologous series of hereditary variability comes down to the following. Related species within one genus, genera within one 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 mutant. Species could also arise through the selection of 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 we now imagine.

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

If nucleic acids in complex with 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. An analogy is observed for all major genetic phenomena:

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

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

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Among the flora globe there is a significant number (more than 2500) species of a group of plants cultivated by humans and called cultural. Cultivated plants and the agrophytocenoses formed by them replaced meadow and forest communities. They are the result of human agricultural activity, which began 7-10 thousand years ago. Wild plants that become cultivated inevitably reflect new stage their lives. The branch of biogeography that studies distribution cultivated plants, their adaptation to soil-climatic conditions in various regions of the globe and including elements of agricultural economics is called geography of cultivated plants.

According to their origin, cultivated plants are divided into three groups:

• the youngest group
• weed species,
• the most ancient group.

Youngest group cultivated plants come from species that still live in the wild. These include fruit and berry crops (apple, pear, plum, cherry), all melons, and some root crops (beets, rutabaga, radishes, turnips).

Weed species plants have become objects of culture where the main crop due to unfavorable natural conditions gave low yields. Thus, with the advancement of agriculture to the north, winter rye replaced wheat; The oilseed crop camelina, widespread in Western Siberia and used to obtain vegetable oil, is a weed in flax crops.

For most ancient cultivated plants cannot be established when their cultivation began, since their wild ancestors have not been preserved. These include sorghum, millet, peas, beans, beans, and lentils.

The need for source material for breeding and improving varieties of cultivated plants led to the creation of the doctrine of their centers of origin. The teaching was based on Charles Darwin’s idea of ​​the existence geographical centers of origin of biological species. The geographical areas of origin of the most important cultivated plants were first described in 1880 by the Swiss botanist A. Decandolle. According to his ideas, they covered quite vast territories, including entire continents. The most important research in this direction, half a century later, was carried out by the remarkable Russian geneticist and botanist-geographer N.I. Vavilov, who studied the centers of origin of cultivated plants on a scientific basis.

N.I. Vavilov proposed a new one, which he called differentiated, a method for establishing the original center of origin of cultivated plants, which is as follows. A collection of the plant of interest collected from all places of cultivation is studied using morphological, physiological and genetic methods. Thus, the area of ​​concentration of the maximum diversity of forms, characteristics and varieties of a given species is determined.

The doctrine of homological series. An important theoretical generalization of N. I. Vavilov’s research is the doctrine of homological series he developed. According to the law of homological series of hereditary variability formulated by him, not only genetically close species, but also genera of plants form homological series of forms, i.e., there is a certain parallelism in the genetic variability of species and genera. Closely related species, due to the great similarity of their genotypes (almost the same set of genes), have similar hereditary variability. If all known variations of characters in a well-studied species are placed in a certain order, then almost all the same variations in character variability can be found in other related species. For example, the variability of ear spinality is approximately the same in soft, durum wheat and barley.

Interpretation by N. I. Vavilov. Species and genera that are genetically close are characterized by similar series of hereditary variability, with such regularity that, knowing the series of forms within one species, one can predict the presence of parallel forms in other species and genera. The closer the relationship, the more complete the similarity in the series of variability.

Modern interpretation of the law. Related species, genera, families have homologous genes and gene orders in chromosomes, the similarity of which is the more complete, the closer the taxa being compared are evolutionarily close. The homology of genes in related species is manifested in the similarity of the series of their hereditary variability (1987).

The meaning of the law.

1. The law of homological series of hereditary variability makes it possible to find the necessary characters and variants in the almost infinite variety of forms of various species of both cultivated plants and domestic animals, and their wild relatives.
2. It makes it possible to successfully search for new varieties of cultivated plants and breeds of domestic animals with certain required characteristics. This is the enormous practical significance of the law for crop production, livestock breeding and breeding.
3. Its role in the geography of cultivated plants is comparable to the role Periodic table elements of D.I. Mendeleev in chemistry. By applying the law of homological series, it is possible to establish the center of origin of plants according to related species with similar characteristics and forms, which probably develop in the same geographical and ecological environment.

Geographical centers of origin of cultivated plants. For the emergence of a large center of origin of cultivated plants, N.I. Vavilov considered a necessary condition, in addition to the richness of wild flora in species suitable for cultivation, the presence of an ancient agricultural civilization. The scientist came to the conclusion that the vast majority of cultivated plants are connected by 7 main geographical centers of their origin:

1. South Asian tropical,
2. East Asian,
3. South-West Asian,
4. Mediterranean,
5. Ethiopian,
6. Central American,
7. Andean.

Outside these centers there was a significant territory that required further study in order to identify new centers of domestication of the most valuable representatives of wild flora. The followers of N.I. Vavilov - A.I. Kuptsov and A.M. Zhukovsky continued research into the study of the centers of cultivated plants. Ultimately, the number of centers and the territory they covered increased significantly, there were 12 of them

1. Sino-Japanese.
2. Indonesian-Indochine.
3. Australian.
4. Hindustan.
5. Central Asian.
6. Near Asian.
7. Mediterranean.
8. African.
9. European-Siberian.
10. Central American.
11. South American.
12. North American

Homologous series in hereditary variability- concept introduced N. I. Vavilov when studying parallelisms in the phenomena of hereditary variability by analogy with homologous series organic compounds.

Law of homologous series: Genetically close species and genera are characterized by similar series of hereditary variability with such regularity that, knowing the series of forms within one species, one can predict the presence of parallel forms in other species and genera.

Patterns in polymorphism in plants, established through a detailed study of the variability of various genera and families, can be conditionally compared to some extent with the homologous series of organic chemistry, for example, with hydrocarbons (CH 4, C 2 H 6, C 3 H 8 ...).

The essence of the phenomenon is that when studying hereditary variability in close groups of plants, similar allelic shapes that were repeated in different species (for example, straw knots cereals With anthocyanin with or without coloring, ears of corn With awn or without, etc.). The presence of such repeatability made it possible to predict the presence of yet undiscovered alleles that are important from the point of view breeding work. The search for plants with such alleles was carried out on expeditions to the supposed centers of origin of cultivated plants. It should be remembered that in those years artificial induction mutagenesis chemicals or exposure ionizing radiation was not yet known, and the search for the necessary alleles had to be done in natural populations.

N.I. Vavilov considered the law he formulated as a contribution to the ideas popular at that time about the natural nature of variability underlying the evolutionary process (for example, the theory nomogenesis L. S. Berg). He believed that hereditary variations that naturally repeat in different groups underlie evolutionary parallelisms and phenomena mimicry.

In the 70-80s of the 20th century he turned to the law of homological series in his works Mednikov B. M., who wrote a number of works in which he showed that precisely this explanation of the emergence of similar, often down to the last detail, characters in related taxa is quite valid.

Related taxa often have related genetic sequences that are slightly different in principle, and some mutations occur with a higher probability and manifest themselves generally similarly in representatives of different, but related, taxa. As an example, a two-variant phenotypically pronounced mutation in the structure of the skull and the body as a whole is given: acromegaly And acromicria, for which a mutation that changes the balance, timely “switching on” or “switching off” during the ontogenesis of hormones is ultimately responsible somatotropin And gonadotropin.

The doctrine of the centers of origin of cultivated plants

The doctrine of the centers of origin of cultivated plants was formed on the basis of the ideas of Charles Darwin (“The Origin of Species,” Chapter 12, 1859) about the existence of geographic centers of origin of biological species. In 1883, A. Decandolle published a work in which he established the geographical areas of the initial origin of the main cultivated plants. However, these areas were confined to entire continents or other fairly large territories. Within half a century after the publication of Decandolle's book, knowledge in the field of the origin of cultivated plants expanded significantly; Monographs were published on cultivated plants from various countries, as well as individual plants. This problem was most systematically developed in 1926-39 by N. I. Vavilov. Based on materials about world plant resources he identified 7 main geographical centers of origin of cultivated plants.

1. South Asian tropical center (about 33% of total number species of cultivated plants).

2. East Asian center (20% of cultivated plants).

3. South-West Asian center (4% of cultivated plants).

4. Mediterranean center (approximately 11% of cultivated plant species).

5. Ethiopian center (about 4% of cultivated plants).

6. Central American center (approximately 10%)

7. Andean (South American) center (about 8%)

Centers of origin of cultivated plants: 1. Central American, 2. South American, 3. Mediterranean, 4. Central Asian, 5. Abyssinian, 6. Central Asian, 7. Hindustan, 7A. Southeast Asian, 8. East Asian.

Many researchers, including P. M. Zhukovsky, E. N. Sinskaya, A. I. Kuptsov, continuing the work of Vavilov, made their own adjustments to these ideas. Thus, tropical India and Indochina with Indonesia are considered as two independent centers, and the South-West Asian center is divided into Central Asian and Western Asian; the basis of the East Asian center is considered to be the Yellow River basin, and not the Yangtze, where the Chinese, as a farming people, penetrated later. Centers of ancient agriculture have also been identified in Western Sudan and New Guinea. Fruit crops (including berries and nuts), having wider distribution areas, go far beyond the centers of origin, more consistent with the ideas of De Candolle. The reason for this lies in its predominantly forest origin (and not in the foothills as for vegetable and field crops), as well as in the peculiarities of selection. New centers have been identified: Australian, North American, European-Siberian.

Some plants were introduced into cultivation in the past outside these main centers, but the number of such plants is small. If previously it was believed that the main centers of ancient agricultural cultures were wide valleys Tiger, Euphrates, Ganga, Nila and other large rivers, Vavilov showed that almost all cultivated plants appeared in the mountainous regions of the tropics, subtropics and temperate zones. The main geographical centers of the initial introduction into culture of most cultivated plants are associated not only with floristic richness, but also with ancient civilizations.

It has been established that the conditions in which the evolution and selection of a crop took place impose requirements on the conditions of its growth. First of all, this is humidity, day length, temperature, and duration of the growing season.

When comparing the characteristics of different 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 homological 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 one species or genus, one can assume the presence of forms with similar combinations of characters within close 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, etc. are known. M. I. Vavilov pointed out that homologous series often extend beyond the boundaries of genera and even families. Short-footedness has been observed in representatives of many mammals: cattle, sheep, dogs, humans. Albinism is observed in all classes of vertebrates.

The law of homological series allows us 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 homological 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 film grains. The naked variety of millet was not known, but the existence of such a form was to be expected, and it was found. Homologous series are based on phenotypic similarity, which arises both as a result of the action of identical alleles of the same gene, and the action of different genes that determine similar chains of sequential 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 systematics makes it possible to find new expected forms. The law directly concerns the study of human hereditary diseases. Issues of treatment and prevention of hereditary diseases cannot be resolved without research on animals with hereditary anomalies similar to those observed in humans. According to the law M. I. Vavilova, phenotypes similar to hereditary human diseases can also be found in animals. Indeed, many pathological conditions identified in animals can be models of hereditary human diseases. So, in dogs there is hemophilia, which is linked to gender. Albinism has been recorded 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. Defects in the structure of the human face, homologous to the “cleft lip” and “cleft palate,” are observed in the facial part of the skull of mice, dogs, and pigs. Mice suffer from hereditary metabolic diseases, such as obesity and diabetes mellitus. In addition to already known mutations, exposure to mutagenic factors can to obtain in laboratory animals many new anomalies similar to those found in humans.