The modern period of breeding development begins with the formation new science- genetics. Genetics is a science that studies the heredity and variability of organisms. A very important contribution to elucidating the essence of heredity was made by G. Mendel (1822-1884), whose experiments on crossing plants underlie most contemporary research by heredity. A Czech by nationality, a monk of the Franciscan monastery in Brunn (now Brno), G. Mendel, at the same time, taught natural sciences at a real school and was very interested in gardening. For many years he devoted all his free time to experiments on crossing various cultivated plants. As a result, patterns of transmission of traits to offspring were discovered. G. Mendel reported his results at a meeting of the "Society of Naturalists" in Brno, and then published them in 1866 in the scientific works of this Society. However, these provisions contradicted the then existing ideas about heredity and therefore received recognition 34 years after their rediscovery.

In 1900, three works appeared simultaneously by three geneticists: Hugo de Vries from Holland, K. Korrens from Germany and E. Cermak from Austria. They confirmed the laws of heredity discovered by G. Mendel.

The published work of de Vries, Correns and Cermak is usually called the rediscovery of Mendel's laws, and 1900 is considered the official date for the beginning of the existence of experimental genetics as an independent science.

Genetics as an independent science was separated from biology at the suggestion of the English scientist Batson in 1907. He also proposed the name of science - genetics.

Since the rediscovery of Mendel's laws, N.P. Dubinin (1986) identifies three stages in the development of genetics.

First step - This is the era of classical genetics, which lasted from 1900 to 1930. It was the time when the theory of the gene and the chromosome theory of heredity were created. The development of the doctrine of the phenotype and genotype, the interaction of genes, the genetic principles of individual selection in breeding, and the doctrine of the mobilization of the genetic reserves of the planet for the purposes of selection were also of great importance. Some of the discoveries of this period deserve special mention.

The German biologist August Weismann (1834-1914) created a theory that in many ways anticipated the chromosome theory of heredity.

Weisman's hypotheses about the meaning of reduction division. In addition, he distinguished between traits that are inherited and traits that are acquired under the influence of external conditions or exercise.

A. Weisman tried to experimentally prove the non-heritability of mechanical damage (over the course of generations, he cut off her tails, but did not get tailless offspring).

Further general concept A. Weisman was refined taking into account cytology data and information about the role of the nucleus in the inheritance of traits. On the whole, he was the first to prove the impossibility of inheritance of traits acquired in ontogeny, and emphasized the autonomy of germ cells, and also showed the biological significance of the reduction in the number of chromosomes in meiosis as a mechanism for maintaining the constancy of the diploid chromosome set of the species and the basis of combinative variability.

In 1901, G. De Vries formulated the mutation theory, which largely coincides with the theory of heterogenesis (1899) by the Russian botanist S. I. Korzhinsky (1861–1900). According to the mutational theory of Korzhinsky - De Vries, hereditary traits are not absolutely constant, but can change abruptly due to changes - mutations of their inclinations.

The most important milestone in the development of genetics - the creation of the chromosome theory of heredity - is associated with the name of the American embryologist and geneticist Thomas Gent Morgan (1866-1945) and his school. Based on fruit fly experiments - Drosophila melanogaster Morgan, by the mid-20s of our century, formed an idea of ​​the linear arrangement of genes in chromosomes and created the first version of the theory of the gene - the elementary carrier of hereditary information. The problem of the gene has become the central problem of genetics. It is being developed at the present time.

The doctrine of hereditary variability was continued in the works of the Soviet scientist Nikolai Ivanovich Vavilov (1887–1943), who in 1920 formulated the law of homological series of hereditary variability. This law summarized a huge amount of material on the parallelism of the variability of closely related genera and species, thus linking systematics and genetics together. The law was a major step towards the subsequent synthesis of genetics and evolutionary doctrine. N. I. Vavilov also created the theory of the genetic centers of cultivated plants, which greatly facilitated the search and introduction of the necessary plant genotypes.

In the same period, some other areas of genetics important for agriculture began to develop rapidly. These include works on studying the patterns of inheritance of quantitative traits (in particular, studies by the Swedish geneticist G. Nilsson-Ehle), on elucidating hybrid power - heterosis (works by American geneticists E. East and D. Jones), on interspecific hybridization of fruit plants (I V. Michurin in Russia and L. Burbank in the USA), numerous studies on private genetics different types cultivated plants and domestic animals.

The development of genetics in the USSR also belongs to this stage. In the post-October years, three genetic schools were formed, headed by prominent scientists - N.K. Koltsov (1872–1940) in Moscow, Yu.A. Filipchenko (1882–1930) and N.I. important role in the development of research in genetics.

Second phase, - This is the stage of neoclassicism in genetics, which lasted from 1930 to 1953. Start second stage can be associated with the discovery of O. Avery in 1944 of the substance of heredity - deoxyribonucleic acid (DNA).

This discovery symbolized the beginning of a new stage in genetics - the birth of molecular genetics, which formed the basis of a number of discoveries in biology of the 20th century.

During these years, the possibility of artificial inducing changes in genes and chromosomes (experimental mutagenesis) was discovered; found that the gene is a complex system, crushed into parts; substantiated the principles of population genetics and evolutionary genetics; biochemical genetics was created, which showed the role of genes for all major biosynthesis in the cell and organism;

The achievements of this period primarily include artificial mutagenesis. The first evidence that mutations can be induced artificially was obtained in 1925 in the USSR by G. A. Nadson and G. S. Filippov in experiments on the irradiation of lower fungi (yeasts) with radium, and decisive evidence for the possibility of experimental obtaining of mutations was given in 1927 d. American Meller's experiments on the effects of X-rays.

Another American biologist J. Stadler (1927) discovered similar effects in plants. Then it was discovered that ultraviolet rays can also cause mutations, and that heat has the same ability, albeit to a weak extent. Soon there was also information that mutations can be caused chemicals. This direction gained wide scope thanks to the research of I. A. Rapoport in the USSR and S. Auerbach in Great Britain. Using the method of induced mutagenesis, Soviet scientists led by A. S. Serebrovsky (1892-1948) began to study the structure of the gene in Drosophila Melanogaster. In their studies (1929-1937) they showed for the first time its complex structure.

At the same stage in the history of genetics, a trend arose and developed that aimed at studying genetic processes in evolution. The fundamental works in this area belonged to the Soviet scientist S. S. Chetverikov (1880–1959), the English geneticists R. Fisher and J. Haldane, and the American geneticist S. Wright. S. S. Chetverikov and his collaborators carried out the first experimental studies of the genetic structure of natural populations on several species of Drosophila. They confirmed the significance of the mutation process in natural populations. Then these works were continued by N. P. Dubinin in the USSR and F. Dobzhansky in the USA.

At the turn of the 1940s, J. Bill (born in 1903) and E. Tatum (1909–1975) laid the foundations of biochemical genetics.

The priority in deciphering the structure of the DNA molecule belongs to the American virologist James Dew Watson (born in 1928) and the English physicist Francis Crick (born in 1916), who published a structural model of this polymer in 1953.

From this moment, namely from 1953, the third stage in the development of genetics begins - the era of synthetic genetics. . Usually this time is called the period of molecular genetics.

Third stage , which began with the construction of a DNA model, continued with the discovery of the genetic code in 1964. This period is characterized by numerous works on deciphering the structure of genomes. So at the end of the 20th century, information appeared about the complete decoding of the Drosophila fly genome, scientists compiled complete map Arabidopsis or small mustard, deciphered by the human genome.

Deciphering only individual sections of DNA already allows scientists to obtain transgenic plants, i.e. plants with introduced genes from other organisms. Such plants, according to some sources, are sown with an area equal to Great Britain. This is mainly corn, potatoes, soybeans. Nowadays, genetics, having broken into many complex areas. Suffice it to mention the achievements of genetic engineering in obtaining somatic and transgenic hybrids, the creation of the first map of the human genome (France, 1992; USA, 2000), the production of cloned sheep (Scotland, 1997), cloned piglets (USA, 2000), etc.

The beginning of the 21st century is called the post-genomic period and, apparently, will be marked by new discoveries in the field of genetics related to the cloning of living beings, the creation of new organisms based on the mechanisms of genetic engineering.

The methods accumulated to date make it possible to decipher the genomes of complex organisms much faster, as well as introduce new genes into them.

Major discoveries in the field of genetics:

1864 - Basic laws of genetics (G. Mendel)

1900 - The laws of G. Mendel were rediscovered ( G. de Vries, K. Correns, E. Cermak)

1900-1903 - Mutation theory (G. de Vries)

1910 - Chromosomal theory of heredity (T. Morgan, T. Boveri, W. Setton)

1925-1938 - "one gene - one protein" (J. Bill, E. Tatum)

1929 - gene divisibility (A.S. Serebrov, N.P. Dubinin)

1925 - artificial mutations (G.A. Nadson, G.S. Filippov)

1944 - DNA - the carrier of hereditary information (O. Avery, K. McLeod)

1953 - structural model of DNA (J. Watson, F. Crick)

1961 – genetic code (M. Nirenberg, R. Holly, G. Khorana)

1961 - operon principle of gene organization and regulation of gene activity in bacteria (F.Jacob, J.Mono)

1959 - gene synthesis (G. Khorana )

1974-1975 - methods of genetic engineering ( K. Murray, N. Murray, W. Benton, R. Davies, E. Sauzen, M. Granstein, D. Hognes)

1978–2000 – sequencing of genomes (F. Blatner, R. Clayton, M. Adams and others)

Genetic methods

HYBRIDOLOGICAL - p an analysis is made of the patterns of inheritance of individual traits and properties of organisms during sexual reproduction, as well as an analysis of the variability of genes and their combinatorics (developed by G. Mendel).

CYTOLOGICAL - with using optical and electron microscopes, the material foundations of heredity at the cellular and subcellular levels (chromosomes, DNA) are studied.

CYTOGENETIC - with the synthesis of hybridological and cytological methods provides the study of the karyotype, changes in the structure and number of chromosomes.

POPULATION-STATISTICAL - about is based on determining the frequency of occurrence of various genes in a population, which makes it possible to calculate the number of heterozygous organisms and thus predict the number of individuals with a pathological (mutant) manifestation of the action of a gene.

BIOCHEMICAL- metabolic disorders (proteins, fats, carbohydrates, minerals) resulting from gene mutations.

MATHEMATICAL - p a quantitative account of the inheritance of traits is made.

GENEALOGICAL - Expressed in the compilation of pedigrees. Allows you to set the type and nature of trait inheritance.

ONTOGENETIC - Allows you to trace the action of genes in the process individual development; in combination with a biochemical method, it allows to establish the presence of recessive genes in a heterozygous state by phenotype.

Genetics is a science that studies two properties of living organisms - heredity and variability. Advances in genetics have great importance for medicine, agriculture and biology.

Heredity

Heredity is understood as the property of organisms to transmit their characteristics and properties to offspring. It is thanks to heredity that one or another breed and type of animal, and variety of plants are preserved in many generations.

Variability

Variability is the property of organisms to acquire new traits that are different from the parent ones. If these signs are fixed in subsequent generations, then they speak of hereditary variability.

Rice. 1. Modification variability.

Variability determines the variety of properties and external data within the same species.

The material carrier of information about the properties of the cell is DNA. It is part of the chromosomes - structures of the cell nucleus that store hereditary information.

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According to modern views of heredity, the differences between species and organisms within a species are determined by differences in the proteins from which organisms are built.

Information about the structure of a particular protein is contained in the gene. A gene is a section of a DNA molecule.

Rice. 2. Gen.

Information is read from genes, which is then implemented when creating protein molecules.

Genotype

Each type of organism is characterized by a certain number and shape of chromosomes - its genotype. For example, a person has 23 pairs of chromosomes in the genotype. Half of the chromosomes are from the father and half from the mother.

Rice. 3. Chromosomal sets.

Sex cells contain a half, or haploid set of chromosomes (n), and somatic cells contain a diploid (2n), or double set.

Phenotype

A trait encoded in a gene may or may not manifest itself, depending on the interaction of genes and the characteristics of environmental conditions. The most common type of interaction between genes is the suppression of the action of one gene by another. All the manifested signs form the phenotype of the organism.

Selection

Selection is closely related to genetics. It is engaged in the creation of new and purposeful changes in existing varieties of plants and animal breeds.

The foundations of genetics and selection are knowledge about the patterns of inheritance of traits and their manifestation in the phenotype.

Many high-yielding varieties of cultivated plants are created by breeders by multiplying the number of chromosomes (3n, 4n, etc.). Such cultures are called polyploids.

What have we learned?

Genetics studies two important properties living organisms: the ability to transfer properties from generation to generation; the ability to acquire new qualities. A separate sign of an organism is a protein, information about the structure of which is encrypted in a gene - a section of a DNA molecule. The genetic foundations of genetics are the theoretical basis for versatile biological and medical research and increasing agricultural productivity.

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Option 10.

QUESTION #1

Genetics is the theoretical basis of selection. Selection. The teachings of N.I. Vavilov about the centers of diversity and origin of cultivated plants. Basic breeding methods: hybridization, artificial selection

Breeding (from the Latin selectio, seligere - selection) is the science of methods for creating highly productive plant varieties, animal breeds and strains of microorganisms.

Initially, selection was based on artificial selection, when a person selects plants or animals with traits of interest to him. Until the XVI-XVII centuries. the selection took place unconsciously, that is, a person, for example, selected the best, largest wheat seeds for sowing, without thinking that he was changing the plants in the direction he needed.

Only in the last century, man, not yet knowing the laws of genetics, began to use selection consciously or purposefully, crossing those plants that satisfied him to the greatest extent.

However, by the method of selection, a person cannot obtain fundamentally new properties in bred organisms, since during selection it is possible to isolate only those genotypes that already exist in the population. Therefore, to obtain new breeds and varieties of animals and plants, hybridization (crossing) is used, crossing plants with desirable traits and, in the future, selecting from the offspring those individuals whose beneficial properties are most pronounced.

Modern selection is a vast area of ​​human activity, which is a fusion of various branches of science, agricultural production and its complex processing. In the course of selection, stable hereditary transformations of various groups of organisms occur. According to the figurative expression of N.I. Vavilov, "... selection is an evolution directed by the will of man." It is known that the achievements of selection were widely used by Charles Darwin in substantiating the main provisions evolutionary theory. Modern selection is based on the achievements of genetics and is the basis of efficient highly productive agriculture and biotechnology.

Tasks of modern breeding

Creation of new and improvement of old varieties, breeds and strains with economically useful features.

Creation of technological highly productive biological systems that maximize the use of raw materials and energy resources of the planet.

Increasing the productivity of breeds, varieties and strains per unit area per unit of time.

Improving the consumer quality of products.

Reducing the share of by-products and their complex processing.

Reducing the share of losses from pests and diseases.

The greatest contribution to the study of the diversity of cultivated plants was made by the Russian breeder N.I. Vavilov.

“I don’t feel sorry for giving my life for the smallest thing in science…”

N.I. Vavilov was born on November 26, 1887 in Moscow. By the time he graduated from a commercial school, he already knew for sure that he would be a biologist. In 1906, Nikolai Ivanovich entered the Moscow Agricultural Institute. Already in his student years, his remarkable qualities began to appear.

In 1913 N.I. Vavilov was sent abroad for scientific work. In Merton (England), in the genetic laboratory of the Horticultural Institute. There he continued his research on the immunity of cereals.

For several months, Nikolai Ivanovich worked in the laboratory of genetics at the University of Cambridge; in France, he visited the largest seed company of Vilmorin, where he got acquainted with the latest achievements selection in seed production, in the susceptibility of various plant varieties. The results of these studies with extensive use of the experiment were summarized in the monograph "Plant Immunity to Infectious Diseases" (1919). In 1917, N. I. Vavilov received an invitation to head the Department of Genetics, Breeding and Private Farming at the Saratov Higher Agricultural Courses and moved to Saratov. At the same time, he continued extensive field study of varieties of various agricultural plants, primarily cereals.

He took an active part in the organization in 1923 of the first All-Union Agricultural Exhibition in Moscow. Vavilov's authority as a scientist and organizer of science grew. In 1924, the Department of Applied Botany and Breeding was transformed into the All-Union Institute of Applied Botany and New Crops under the Council of People's Commissars (since 1930 - the All-Union Institute of Plant Growing VIR), and N. I. Vavilov was approved as its director. By the end of the 1920s, the All-Union Institute of Applied Botany and New Cultures had become one of the largest and most famous in the world. scientific centers for the study of cultivated plants. Vavilov devoted all his energy to raising agriculture to a new level. Dying of starvation in the Gulag, he thought about his homeland, about all of humanity. In an effort to prove the need for science - genetics, capable of creating new varieties of plants that will save humanity from hunger and satisfy the growing need for food. The bright and wonderful life of Nikolai Ivanovich will long attract the attention of researchers. Our youth should know this great life, which can be called the feat of a scientist, should learn from it how to work selflessly and how to love their homeland and science.

The teachings of N.I. Vavilov on the origin of cultivated plants

The doctrine of the source material is the basis of modern breeding. The source material serves as a source of hereditary variability - the basis for artificial selection. N.I. Vavilov established that there are areas on Earth with a particularly high level of genetic diversity of cultivated plants, and identified the main centers of origin of cultivated plants.

Centers of origin of cultivated plants

For each center, the most important agricultural crops characteristic of it have been established.

1. Tropical center - includes the territories of tropical India, Indochina, South China and the islands of Southeast Asia. At least one quarter of the world's population still lives in tropical Asia. In the past, the relative population of this territory was even more significant. About one third of the currently cultivated plants originate from this center. It is the birthplace of plants such as rice, sugarcane, tea, lemon, orange, banana, eggplant, and also a large number tropical fruits and vegetables.

2. East Asian center - includes temperate and subtropical parts of Central and East China, Korea, Japan and most of about. Taiwan. Approximately one quarter of the world's population also lives in this territory. About 20% of the world's cultural flora originates from East Asia. This is the birthplace of such plants as soybeans, millet, persimmons, and many other vegetable and fruit crops.

3. Southwest Asian center - includes the territories of the inner upland Asia Minor (Anatolia), Iran, Afghanistan, Central Asia and Northwestern India. The Caucasus also adjoins here, the cultural flora of which, as studies have shown, is genetically related to Western Asia. Homeland of soft wheat, rye, oats, barley, peas, melons.

This center can be subdivided into the following foci:

a) Caucasian with many original types of wheat, rye and fruit. For wheat and rye, as shown by comparative studies, this is the most important world focus of their species origin;

b) Western Asia, including Asia Minor, Inner Syria and Palestine, Transjordan, Iran, Northern Afghanistan and Central Asia together with Chinese Turkestan;

c) North-West Indian, including, in addition to the Punjab and the adjacent provinces of North India and Kashmir, also Balochistan and Southern Afghanistan.

4. Mediterranean center - includes countries located along the shores of the Mediterranean Sea. This remarkable geographical center, characterized in the past by the greatest ancient civilizations, gave rise to approximately 10% of cultivated plant species. Among them are durum wheat, cabbage, beets, carrots, flax, grapes, olives, and many other vegetable and fodder crops.

5. Abyssinian center. Total number species of cultivated plants associated in their origin with Abyssinia does not exceed 4% of the world's cultural flora. Abyssinia is characterized by a number of endemic species and even genera of cultivated plants. Among them are such as coffee tree, watermelon, cereal. Within the New World, an amazingly strict localization of the two centers of speciation of the main cultivated plants has been established.

6. Central American center covering a vast territory North America including southern Mexico. Three centers can be distinguished in this center:

a) Mountain southern Mexican,

b) Central American,

c) West Indian island.

About 8% of various cultivated plants originate from the Central American center, such as corn, sunflower, American long-staple cotton, cocoa (chocolate tree), a number of beans, pumpkins, many fruits (guayava, anone and avocado).

7. Andean center, within South America, confined to the Andean ridge. This is the birthplace of potatoes and tomatoes. This is where the cinchona tree and the coca bush originate. As you can see from the list geographical centers, the initial introduction into the culture of the vast majority of cultivated plants is associated not only with floristic areas that are distinguished by rich flora, but also with ancient civilizations. Only comparatively few plants were introduced in the past into cultivation from the wild flora outside the listed main geographical centers. The seven indicated geographical centers correspond to the most ancient agricultural cultures.

The South Asian tropical center is associated with a high ancient Indian and Indochinese culture. The latest excavations have shown the deep antiquity of this culture, synchronous with the Central Asian. The East Asian center is associated with ancient Chinese culture, and the Southwest Asian center is associated with the ancient culture of Iran, Asia Minor, Syria, Palestine and Assyro-Babylonia. The Mediterranean for many millennia BC concentrated the Etruscan, Hellenic and Egyptian cultures. The peculiar Abyssinian culture has deep roots, probably coinciding in time with the ancient Egyptian culture. Within the New World, the Central American Center is associated with the great Mayan culture, which reached great success in science and art before Columbus. Andean Center in South America combined in development with the remarkable pre-Inca and Inca civilizations.

Collection samples collected under the guidance of N.I. Vavilov, were kept in Leningrad at the All-Union Institute of Plant Industry (VIR), created by N.I. Vavilov in 1930. On the basis of the All-Union Institute of Applied Botany and New Cultures (formerly the Department of Applied Botany and Breeding, even earlier - the Bureau of Applied Botany).

During the years of the Great Patriotic War during the siege of Leningrad, VIR employees were on duty around the clock at the collection of seeds of grain crops. Many VIR employees died of starvation, but the invaluable species and varietal wealth, from which breeders around the world still draw material to create new varieties and hybrids, was preserved.

In the second half of the 20th century, new expeditions were organized to collect samples to replenish the VIR collection; at present, this collection includes up to 300,000 plant specimens belonging to 1,740 species.

Law of homologous series of hereditary variability

“Genetically close genera and species 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 related species and genera.”

N.I. Vavilov found that "an important point in assessing the material for selection is the presence in it of a variety of hereditary forms."

Diversity of genes and genotypes in N.I. Vavilov called the genetic potential of the source material.

Systematizing the doctrine of the source material, N.I. Vavilov formulated the law of homological series (1920):

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.

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

According to this law, genetically close species and genera have similar genes that give similar series of multiple alleles and trait variants. For example, within different genera of cereals, there is a parallel variability in grain color:

Theoretical and practical significance of the law of homologous series:

N.I. Vavilov clearly distinguished between intraspecific and interspecific variability. At the same time, the species was considered as an integral, historically established system.

N.I. Vavilov showed that intraspecific variability is not unlimited and is subject to certain laws.

The law of homologous series is a guide for breeders to predict the possible variations of traits.

N. I. Vavilov was the first to carry out a targeted search for rare or mutant alleles in natural populations and populations of cultivated plants. Nowadays, the search for mutant alleles to increase the productivity of strains, varieties and breeds continues.

This law may help rational use organic wealth of the earth. The law of homologous series is recognized as one of the fundamental laws of wildlife. It facilitates the search for the economic traits of plants and animals necessary for breeding.

Selection Methods

Modern breeding uses a whole range of methods based on the latest achievements of many sciences: genetics, cytology, botany, zoology, microbiology, agroecology, biotechnology, information technologies etc. However, hybridization and artificial selection remain the main specific methods of selection.

Hybridization

Crossing organisms with different genotypes is the main method for obtaining new combinations of traits. Sometimes hybridization is necessary, for example, to prevent inbreeding depression. Inbreeding depression is manifested during closely related crossing and is expressed in a decrease in productivity and vitality. Inbreeding depression is the opposite of heterosis.

There are the following types of crosses:

Intraspecific crosses - different forms are crossed within a species. Intraspecific crossings also include crossings of organisms of the same species living in different ecological conditions and / or in different geographical areas (ecological-geographical crossings). Intraspecific crosses underlie most other crosses.

Closely related crosses - inbreeding in plants and inbreeding in animals. They are used to obtain clean lines.

Interline crosses - representatives of pure lines are crossed (and in some cases - different varieties and breeds). Interline crossings are used to suppress inbreeding depression, as well as to obtain the effect of heterosis.

Crossings (back-crosses) are crossings of hybrids (heterozygotes) with parental forms (homozygotes). For example, crosses of heterozygotes with dominant homozygous forms are used to prevent the phenotypic expression of recessive alleles.

Analyzing crosses (they are a kind of back-crosses) are crosses of dominant forms with an unknown genotype and recessive-homozygous tester lines. Such crosses are used to analyze sires by offspring.

Saturating (replacement) crosses are also a type of backcrosses. With multiple backcrosses, selective (differential) substitution of alleles (chromosomes) is possible.

Distant crosses - interspecific and intergeneric. Usually, distant hybrids are sterile and are propagated vegetatively; to overcome the infertility of hybrids, doubling the number of chromosomes is used, in this way amphidiploid organisms are obtained: rye-wheat hybrids (triticale), wheat-couch grass hybrids.

Somatic hybridization is hybridization based on the fusion of somatic cells of completely dissimilar organisms.

Artificial selection has been and remains the most important selection method. However, the selection process includes two groups of activities: evaluation of the source material and selective reproduction (reproduction) of the selected organisms or their parts.

Selection is the process of differential (unequal) reproduction of genotypes. At the same time, one should not forget that, in fact, selection is carried out according to phenotypes at all stages of the ontogeny of organisms (individuals). The ambiguous relationship between genotype and phenotype involves testing selected plants for progeny.

There are many forms of artificial selection. Let us consider in more detail the most commonly used forms of selection.

Mass selection - the entire group is subjected to selection. For example, seeds from the best plants are combined and sown together. Mass selection is considered a primitive form of selection, since it does not allow eliminating the influence of modification variability. Used in seed production. It is recommended for the selection of new plants introduced into the culture or crops that are not well developed in terms of breeding.

Let us consider the methods for evaluating the source material using plants as an example.

In the process of selection, the material is evaluated according to its economic and biological properties, which are the object of selection. But regardless of the characteristics of the object and the tasks of selection, the material is evaluated according to the following criteria:

A certain rhythm of development corresponding to the soil and climatic conditions in which the further exploitation of the variety is planned;

High potential productivity with high product quality;

Resistance to the adverse effects of physical and chemical environmental factors (frost resistance, heat resistance, drought resistance, resistance to various types of chemical pollution);

resistance to diseases and pests;

Responsiveness to agricultural technology.

Ideally, the variety should not meet individual requirements, but their complex. However, in practice this often turns out to be impossible, and that is why the creation of compositions consisting of lines (clones) with different hereditary properties is considered the fastest and most reliable way to increase the overall sustainability of agro ecosystems.

selection hybridization artificial selection

QUESTION #2

Species and spatial structure of ecosystems. Food connections, cycling of substances and energy conversion in ecosystems

c) Muller

b) Schmalhausen

d) Kovalevsky

The structure of the ecosystem is multifaceted. Distinguish between species and spatial structure.

The species structure of an ecosystem is the diversity of species, the relationship and ratio of their numbers. The various communities that make up an ecosystem are made up of different number species - species diversity. In the taiga forest, on an area of ​​100 m, as a rule, plants of about 30 different species grow, and in a meadow along the river - twice as many.

Species diversity depends on the ratio of the number of species in the ecosystem. For example, 1000 birds live in a suburban forest: 100 individuals of 10 different species each. In another suburban forest there are also 1000 birds of the same 10 species, but 920 of the birds are crows and jackdaws (two species), and individuals of the remaining 8 species are much less common, on average 10 individuals.

The decrease in species diversity threatens the very existence of the species due to the reduction of genetic diversity - the stock of recessive alleles that ensures the adaptability of populations to changing environmental conditions.

In turn, species diversity serves as the basis for ecological diversity - the diversity of ecosystems. The totality of genetic, species and ecological diversity makes up the biological diversity of the planet.

Spatial structure of the ecosystem.

Populations of different species in an ecosystem are distributed in a certain way - they form a spatial structure. There are vertical and horizontal structures of the ecosystem.

Vegetation forms the basis of the vertical structure.

The plant community determines, as a rule, the appearance of the ecosystem. Plants largely influence the conditions for the existence of other species. In the forest, these are large trees, in the meadows and in the steppes - perennial grasses, and in the tundra, mosses and shrubs dominate.

Living together, plants of the same height create a kind of floors - tiers. In the forest, for example, tall trees make up the first (upper) tier, the second tier is formed from young trees of the upper tier and from adult trees, smaller in height. The third tier consists of shrubs, the fourth - of tall grasses. The lowest tier, where very little light enters, is made up of mosses and undersized grasses.

Layering is also observed in herbaceous communities (meadows, steppes, savannahs). There is also an underground layering, which is associated with different depths of penetration into the soil of the root systems of plants: in some, the roots go deep into the soil, reach the groundwater level, while others have a surface root system that captures water and nutrients from the upper soil layer.

Animals are also adapted to life in one or another plant layer (some do not leave their layer at all).

Any community can be represented as a food web in which numerous food chains are intricately intertwined. Food chains transfer substances and energy in the ecosystem from link to link. Each link in the food chain is called a trophic (from the Greek trofo - food) level.

The first trophic level is made up of producers, autotrophic organisms - plants and some bacteria. Basically, plants create organic substances from inorganic substances by using the energy of sunlight (photosynthesis), and bacteria - by using energy. chemical reactions oxidation of mineral substances (chemosynthesis).

The second trophic level is made up of herbivorous animals - consumers. The third level is carnivores (predators), the fourth level is animals that eat other carnivores, etc. Many animals cannot be attributed to one level, since they are omnivores, they can receive energy from several different trophic levels.

A variety of substances and energy move from one trophic level to another along the food chains as some organisms are eaten by others, undergoing numerous transformations. At the final stage, decomposers completely destroy organic substances, turning them into minerals.

This means that the existence of all ecosystems depends on a constant influx of energy from outside. How is it carried out energy metabolism in ecosystems?

All organisms need energy, and the only source of almost all energy on Earth is the Sun. However, only 1% of the sun's light energy is captured by plants during photosynthesis and stored as chemical energy, while 99% is lost as heat and spent on evaporation. The energy stored by plants is transferred from one trophic level to another along the food chain. Part of the energy is lost during the transformation of food substances into molecules of the predator's body, and part passes through the intestinal tract of the predator unchanged.

Haeckel-Muller biogenetic law (also known as "Haeckel's law", "Müller-Haeckel's law", "Darwin-Muller-Haeckel's law", "basic biogenetic law"): each Living being in its individual development (ontogenesis) it repeats to a certain extent the forms passed by its ancestors or its species (phylogeny).

He played an important role in the history of the development of science, but was later refuted and in its original form is not recognized by modern biological science.

Biogenetic Law, one of the generalizations of evolutionary biology, linking individual development, or ontogenesis, with historical development, or phylogeny. The biogenetic law established by the German scientists F. Müller (1864) and E. Haeckel (1866) states that the ontogenesis of any organism is a brief repetition (recapitulation) of the main stages of the phylogenesis of the species to which the given organism belongs.

The biogenetic law finds many confirmations in the data of comparative anatomy, embryology and paleontology. For example, in the embryos of birds and mammals, at a certain stage of embryonic development, the rudiments of the gill apparatus appear. This is because terrestrial vertebrates evolved from gill-breathing fish-like ancestors. Based on the biogenetic law and using embryological data, it is possible to recreate the course historical development certain groups of organisms. This is especially important in those cases when for k.-l. group, fossil remains of ancestral forms are unknown, i.e., with the incompleteness of the paleontological record.

The Haeckel-Muller biogenetic law: each individual in its individual development (ontogeny) briefly and concisely repeats the history of the development of its species (phylogenesis).

a) Examples in animals:

* The vessels of the embryos of land vertebrates are similar to the vessels of fish;

* The human fetus has gill slits.

* Butterfly caterpillars and beetle larvae are similar to annelids.

* Tadpoles of amphibians are similar to fish.

b) Examples in plants:

* Kidney scales in the bud of plants develop like leaves.

* The petals of the buds are green at first, acquire their characteristic color.

* From the moss spores, a green thread first appears, similar to filamentous algae (pre-sprout).

c) Amendments to the biogenetic law.

* In embryos, the repetition of phylogenesis may be disturbed in connection with adaptations to living conditions in ontogeny. Appear: embryonic membranes, yolk sac in fish eggs, external gills in a tadpole, cocoon in a silkworm.

* Ontogeny does not fully reflect phylogeny due to the appearance of mutations that change the course of development of the embryo (in the embryo of a snake, all the vertebrae are laid at once, i.e. their number does not increase gradually; in birds, the five-fingered stage of limb development fell out, 4 fingers are laid in the embryo, and not 5, only 3 fingers grow in the wing).

* In ontogenesis, the embryonic stages of development are repeated, and not adult forms (the Lancelet repeats in ontogeny the general stages with a free-swimming ascidian larva, and not with its adult, fixed form).

d) Modern ideas about the biogenetic law.

* Severtsov showed that due to changes in development, some stages of development of the embryo can fall out; there are changes in the organs of the embryo that were not in the ancestors; new species emerge; new signs are revealed (for example, tailed (newts) and tailless (frogs) amphibians descended from one ancestor: the newt larva is long, because it has many vertebrae, the number of vertebrae in the frog larva has decreased due to mutation; the lizard embryo has fewer vertebrae, than in the snake embryo, due to developmental mutations).

QUESTION #3

The human races are:

a) three biological species

b) different populations of the same species

c) different populations of different species

View Homo sapiens is divided into three big races: Eurasian (Caucasoid), Asian-American (Mongoloid) and Australo-Negroid (Equatorial). Representatives of the Caucasian race are characterized by relatively fair skin, soft straight or wavy hair, thin lips, and a narrow protruding nose. Men usually grow beards and mustaches well. Within the race, there is great variability in hair and eye color, so it is divided into three large parts: light-colored northern (Scandinavians), dark-colored southern (Indians, Arabs) and Central European with an intermediate type of pigmentation.

Typical representatives of the Mongoloid race have dark skin of a yellowish tint, dark brown eyes, dark and straight coarse hair. In men, the hairline on the body is poorly developed. Most Mongoloids are characterized by epicanthus - a special fold of the upper eyelid that covers the inner corner of the eye. The nose is rather narrow. Representatives of the equatorial race are characterized by black curly hair, very dark skin and brown eyes. Beards and mustaches in men grow weakly. The nose is rather flat, slightly protruding, with wide wings. Most representatives have thick lips and a protruding jaw region of the skull.

Major human races

In modern humanity, there are three main races: Caucasoid, Mongoloid and Negroid. These are large groups of people that differ in some physical features, such as facial features, skin color, eyes and hair, hair shape. Each race is characterized by the unity of origin and formation in a certain territory.

Belongs to the European race indigenous people Europe, South Asia and North Africa. Caucasoids are characterized by a narrow face, a strongly protruding nose, and soft hair. The skin color of northern Caucasians is light, while that of southern Caucasians is predominantly swarthy.

TO Mongoloid race includes the indigenous population of Central and East Asia, Indonesia, Siberia. Mongoloids are distinguished by a large, flat, wide face, slit eyes, hard, straight hair, and dark skin color.

In the Negroid race, two branches are distinguished - African and Australian. For negroid race dark skin color, curly hair, dark eyes, wide and flat nose are characteristic.

Racial features are hereditary, but at present they are not essential for human life. Apparently, in the distant past, racial traits were useful for their owners: the dark skin of blacks and curly hair, creating an air layer around the head, protected the body from the action of sunlight, the shape of the facial skeleton of the Mongoloids with a larger nasal cavity, perhaps, is useful for heating cold air before it enters the lungs. According to mental abilities, i.e., the ability to know, creative and in general labor activity All races are the same. Differences in the level of culture are associated not with the biological characteristics of people of different races, but with the social conditions for the development of society. Initially, some scholars confused the level social development with biological features and tried among modern peoples to find transitional forms that connect man with animals. These mistakes were used by the racists, who began to talk about the alleged inferiority of some races and peoples and the superiority of others to justify the merciless exploitation and direct destruction of many peoples as a result of colonization, the seizure of foreign lands and the outbreak of wars.

The failure of racism is proved by the real science of races - racial science. Racial science studies racial characteristics, the origin, formation and history of human races. The data obtained by racial science indicate that the differences between races are not sufficient to consider races as different biological species of people. Mixing of races - miscegenation - occurred constantly, as a result of which intermediate types arose at the boundaries of the ranges of representatives of different races, smoothing out the differences between races.

QUESTION #4

Butterfly caterpillars are similar to annelids - this is evidence of evolution from the field of science:

a) biogeography b) embryology

c) comparative anatomy d) paleontologists

Paleontological evidence for evolution

Paleontology is the science of the organic world of past geological epochs, that is, of organisms that once lived on Earth and are now extinct. In paleontology, paleozoology and paleobotany are distinguished.

Paleozoology studies the remains of fossil animals, while paleobotany studies the remains of fossil plants. Paleontology directly proves that the organic world of the Earth in different geological epochs was different, it changed and developed from primitive forms of organisms to more highly organized forms. Paleontological studies make it possible to establish the history of the development of various forms of organisms on Earth, to identify related (genetic) relationships between individual organisms, which contributes to the creation natural system organic world of the Earth. To substantiate the theory of evolution, Charles Darwin widely used numerous evidence from the field of paleontology, biogeography, and morphology. Subsequently, facts were obtained that recreate the history of the development of the organic world and serve as new evidence of the unity of the origin of living organisms and the variability of species in nature.

Paleontological finds are perhaps the most convincing evidence of the evolutionary process. These include fossils, imprints, fossils, fossil transitional forms, phylogenetic series, sequence of fossil forms. Let's consider some of them in more detail.

Fossil transitional forms are forms of organisms that combine features of older and younger groups. Among plants, psilophytes are of particular interest. They originated from algae, were the first of the plants to make the transition to land and gave rise to higher spore and seed plants. Seed ferns are a transitional form between ferns and gymnosperms, and cycads are between gymnosperms and angiosperms.

Among the fossil vertebrates, forms can be distinguished that are transitional between all classes of this subtype. For example, the oldest group of lobe-finned fish gave rise to the first amphibians - stegocephals. This was possible thanks to characteristic structure the skeleton of paired fins of lobe-finned fish, which had anatomical prerequisites for their transformation into five-fingered limbs of primary amphibians. Forms are known that form the transition between reptiles and mammals. These include animal lizards (foreigners). And the link between reptiles and birds was the first bird (Archeopteryx).

Paleontological series - series of fossil forms related to each other in the process of evolution and reflecting the course of phylogenesis (from the Greek phylon - genus, tribe, genesis - origin). The evolution of the horse is a classic example of the use of a series of fossil forms to elucidate the history of a particular group of animals. Russian scientist V.O. Kovalevsky (1842-1883) showed the gradual evolution of the horse, establishing that successive fossil forms became more and more similar to modern ones.

Modern one-toed animals descended from small five-toed ancestors that lived in forests 60-70 million years ago. Climate change has led to an increase in the area of ​​​​the steppes and the settlement of horses on them. Movement on long distances in the search for food and in protection from predators contributed to the transformation of the limbs. In parallel, the size of the body, jaws increased, the structure of the teeth became more complicated, etc.

To date, a sufficient number of paleontological series (proboscis, carnivores, cetaceans, rhinos, some groups of invertebrates) are known, which prove the existence of an evolutionary process and the possibility of the origin of one species from another.

In conclusion, we can conclude that the briefly considered phenomena prove that the organic world of the Earth is in a state of constant slow gradual development, i.e. evolution, while development has gone and goes from simple to complex.

QUESTION #5

A scientist who had a metaphysical view of evolution:

a) C. Linnaeus b) Lamarck

c) C. Darwin d) A. Wallace

The evolutionary idea - as the idea of ​​the historical development of wildlife and the variability of species, originated a very long time ago. In the II-I millennia BC. in China and India, there were teachings about the possibility of transforming some living beings into others, about the origin of man from monkeys. Thoughts about the natural development of all living beings from primary matter are found among philosophers Ancient Greece Heraclitus and Aristotle.

However, between the evolutionary ideas of ancient thinkers and modern scientists, the similarity is purely external. The views of ancient thinkers had the character of conjectures, without strict scientific justification facts. Ancient civilizations in Europe were replaced by the Middle Ages. The prevailing idea was the immutability of all life on Earth.

Evolutionary ideas took shape in the form of a doctrine only with the emergence of a materialistic worldview in philosophy. The idealistic worldview that prevailed until then proclaimed that God was the creator of all nature. And according to the materialistic doctrine, the inanimate initially arose, and then nature and in the course of its long development highly evolved beings emerged. No one created them, they are the result of evolutionary transformations of matter, the peak of which was man.

With the accumulation of scientific information, views in philosophy change - a materialistic doctrine is formed; in biology, the first ideas about evolution appear, which were already contained in the later works of K. Linnaeus, and then the evolutionary doctrine of J.-B. Lamarck (XVIII-XIX centuries).

in Russia in the 18th century. evolutionary ideas were formed, which were reflected in the works of M. V. Lomonosov and A. N. Radishchev. In the 19th century, K. M. Baer made a great contribution to science with studies of the embryonic development of animals; the laws developed by him were noted by Ch. Darwin and called "the law of germinal similarity." The zoologist K. F. Roulier substantiated the position on the relationship between the organism and the external environment. After analyzing the importance of heredity and variability as conditions for the adaptation of species to the environment, he came to the conclusion that this is a gradual, evolutionary process. In the classic work of A. I. Herzen "Letters on the Study of Nature" it is argued that matter is not created or destroyed by anyone, and all its forms and properties are the product of its development.

Contribution to science by C. Linnaeus (1707-1778)

He discovered about 1.5 thousand plant species; - described about 10 thousand plant species and about 4.5 thousand animal species;

Developed short and clear definitions of each group of organisms, which greatly facilitated their description; - Defined the concept of "kind".

He introduced Latin into science and a convenient binary (double) nomenclature instead of the cumbersome polynomial names used earlier; this nomenclature is used in our time ("The System of Nature", 1735);

Developed the principles for constructing a classification of wildlife ("Philosophy of Botany"). On these principles, he built a new scientific system of living nature, which included all animals and all plants known at that time and was the most perfect for that time;

in streamlining rapidly accumulating knowledge led to the need to systematize them. Practical dependences are created on their benefit to a person or the harm they bring.

K. Linnaeus created the most perfect system of the organic world for that time, including in it all the then known animals and plants. In many cases, he correctly combined the types of organisms according to the similarity of the structure. The system of K. Linnaeus was artificial, since it did not reflect the relationship and similarity of plants and animals in terms of the totality of essential structural features, did not indicate the unity of the origin of living organisms. K. Linnaeus was aware of the artificiality of his system and pointed out the need to develop a natural system of nature. He wrote: "An artificial system serves only until a natural one is found."

According to his worldview, K. Linnaeus was a metaphysician and a creationist. According to metaphysical ideas, nature is something frozen, not changing in time. During the reign religious beliefs scientists believed that the types of organisms were created independently of each other by the Creator and are immutable. “There are so many types,” K. Linnaeus noted, “how many different forms the Almighty created at the beginning of the world.” That's why the search natural nature meant for biologists attempts to penetrate into the plan of creation, which was guided by God, creating all life on earth.

LIST OF USED LITERATURE

1. Sivoglazov N.I., Agafonova I.B., Zakharova E.T. General biology. A basic level of. 10 - 11 class. - M.: Bustard, 2005.

2. Belyaev D.K. General biology: tutorial for grades 10-11 of educational institutions / P.M. Borodin, N.N. Vorontsov and others - Moscow: Education, 2002.

3. Sivkova V.V. New directory student grade 5-11. Universal allowance. Publishing house "Ves", St. Petersburg - 2002.

4. Anastasova L.P. and others. "Man and the Environment" (M., "Enlightenment", 1981) Grade 9

5. Morozov E.I., Tarasevich E.I., Anokhina V.S. Genetics in questions and answers. Minsk. "University". 1989.

6. Fogel F., Motulski A. Human genetics. Moscow. "Peace". 1990.

7. Demyanenkov E.N. Biology in questions and answers. - Moscow, 1996.

8. Korotkova L.S. Didactic material on general biology grade 10. Moscow "Enlightenment" 1984

9. Nikeshov A.I. Schoolchildren's guide to biology grades 6-9.

Moscow "Drofa" 1996

10. Dmitrieva T.A. Didactic materials: Biology. Human. General biology. M Bustard 2002

REVIEW

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Lesson in the 9th grade “Genetic bases of selection of organisms. Tasks of modern selection»

Target: to give the concept of selection, its methods, goals and results, to show that the theoretical basis of selection is genetics.

Equipment and material: tables depicting animal breeds and plant varieties.

Basic concepts and terms: selection, artificial selection, breed, variety, strain, zoning, hybridization, unconscious selection, methodical selection, mass selection, individual selection.

Structure and content of the lesson

1. Actualization of basic knowledge and motivation learning activities

Questions for students.
1) What varieties of plants and breeds of animals do you know?
2) How did breeders get these varieties and breeds?
3) thanks to what breeders get such a variety of varieties?
4) Can knowledge about the genetic characteristics of organisms contribute to the selection process?

2. Learning new material

Teacher's story.
Tasks and methods of modern breeding.
Breeding is the science of methods for creating plant varieties, animal breeds and strains of microorganisms with traits that a person needs. She achieved the most significant success with the active use of the achievements of genetics, which was the theoretical basis of selection. In the selection process, as a rule, there are several stages:
Substantiation of the purpose and objectives of selection;
Creation and selection of source material;
Development of a breeding scheme, breeding process (including a variety of breeding methods);
Variety testing.
The emergence of scientific selection is associated with the evolutionary teachings of Charles Darwin, experimental studies G. Mendel, V. Johansen, breeders I. V. Michurin, L. Burbank, whose work served as the basis for the development of the theory of selection. In turn, the discovery in genetics contributed to the development of methods of the selection process and to an increase in the efficiency of artificial selection. For example, the discoveries of Mendel's laws made it possible to purposefully select pairs for crossing, and the establishment by N. I. Vavilov of the centers of origin of cultivated plants and the justification of the law of homologous series of hereditary variability made it possible for breeders to develop methods for effectively searching for the source material. The study of the nature of the inheritance of economically valuable traits contributed to the creation of a whole system of crosses and made it possible to combine various properties of plants.
N. I. Vavilov did a lot to develop the theoretical foundations of selection and to clarify the definition of selection as an independent science. Giving general definition selection as a science, N. I. Vavilov wrote: “Selection is essentially human intervention in the shaping of animals and plants; in other words, selection is evolution directed by the will of man "N. I. Vavilov emphasized a high degree the complexity of breeding as a scientific discipline and believed that it consists of:
Teachings about source material;
Teachings about hereditary variability;
Teachings about the role of the environment in identifying varietal characteristics;
Theories of hybridization;
Theories of the selection process;
The doctrine of the main directions in selection work (for example, selection is not immunity);
Private selection.
The use of various methods in the breeding process led to the creation of a new direction - synthetic breeding. It is based on the use of source material created by hybridization of various varieties and forms. The basis of synthetic selection is recombination and transgression. In combination synthetic breeding, in one hybrid plant, the characteristics and properties of two or more parental forms are combined. The task of the breeder is to select and genetically stabilize hybrid plants that combine these traits and properties most successfully. Transgressive synthetic selection is based on selection in individuals splitting after hybridization of a generation with transgressions, i.e., with positive traits that are more pronounced than in parents. The success of transgressive synthetic selection depends on the correct identification of parental pairs capable of producing transgressions when crossed.
Presentation of material about plant varieties, animal breeds, strains of microorganisms.
A story about the forms of artificial selection.

3. Generalization, systematization and control of knowledge and skills of students

Conversation.
1) Name the industries practical application genetics.
2) List the main tasks of modern breeding.
3) What role does the diversity of the initial breeding material play for breeding?
4) Define: what is a variety?

4. Independent work students

Give answers to questions.
1) What is the mechanism of artificial selection?
2) What are called strains?
3) What is the name of a set of measures aimed at checking the compliance of the properties of certain breeds or varieties with the conditions of a certain natural zone?
5) Why varieties and breeds cannot be called species?

5. Homework

Selection is the science of creating new and improving existing breeds of animals, plant varieties, strains of microorganisms. Selection is based on methods such as hybridization and selection. The theoretical basis of selection is genetics. The development of selection should be based on the laws of genetics as a science of heredity and variability, since the properties of living organisms are determined by their genotype and are subject to hereditary and modification variability. It is genetics that paves the way for effective management of heredity and variability of organisms. At the same time, selection is also based on the achievements of other sciences:

• taxonomy and geography of plants and animals,
• cytology,
• embryology,
• biology of individual development,
• molecular biology,
• physiology and biochemistry.

The rapid development of these areas of natural science opens up completely new perspectives. Already today, genetics has reached the level of purposeful design of organisms with the desired features and properties. Genetics plays a decisive role in solving almost all breeding problems. It helps rationally, on the basis of the laws of heredity and variability, to plan the selection process, taking into account the characteristics of the inheritance of each specific trait.

For successful solution tasks facing selection, Academician N.I. Vavilov emphasized the meaning:

• study of varietal, species and generic diversity of crops;
• study of hereditary variability;
• the influence of the environment on the development of traits of interest to the breeder;
• knowledge of the patterns of inheritance of traits during hybridization;
• features of the selection process for self- or cross-pollinators;
• artificial selection strategies.

Breeds, varieties, strains- populations of organisms artificially created by man with hereditarily fixed features:

• productivity
• morphological,
• physiological signs.

Each animal breed, plant variety, strain of microorganisms is adapted to certain conditions, therefore, in each zone of our country there are specialized variety testing stations and breeding farms for comparing and testing new varieties and breeds. Selection work begins with the selection of source material, which can be used as cultivated and wild forms of plants.

In modern breeding, the following main types and methods of obtaining the source material are used.

natural populations. This type of source material includes wild forms, local varieties of cultivated plants, populations and accessions presented in the VIR world collection of agricultural plants.

hybrid populations, created as a result of crossing varieties and forms within the same species (intraspecific) and obtained as a result of crossing different species and genera of plants (interspecific and intergeneric).

Self-pollinated lines (incubation lines). In cross-pollinating plants, an important source of starting material is self-pollinated lines obtained by repeated forced self-pollination. The best lines are crossed with each other or with varieties, and the resulting seeds are used for one year to grow heterotic hybrids. Hybrids created on the basis of self-pollinated lines, unlike conventional hybrid varieties, need reproduce annually.

Artificial mutations and polyploid forms. This type of source material is obtained by exposing plants to various types of radiation, temperature, chemicals and other mutagenic agents.

At the All-Union Institute of Plant Industry N.I. Vavilov collected a collection of varieties of cultivated plants and their wild ancestors from all over the globe, which is currently being replenished and is the basis for breeding any crop. The richest in the number of cultures are the ancient centers of civilization. It is there that the earliest culture of agriculture is carried out, artificial selection and plant breeding are carried out for a longer time.

Classical methods of plant breeding were and still are hybridization and selection. There are two main forms of artificial selection: mass and individual.

Mass selection used in breeding cross-pollinated plants (rye, corn, sunflower). In this case, the variety is a population of heterozygous individuals, and each seed has a unique genotype. With the help of mass selection, varietal qualities are preserved and improved, but the selection results are unstable due to random cross-pollination.

Individual selection used in the selection of self-pollinated plants (wheat, barley, peas). In this case, the offspring retains the characteristics of the parental form, is homozygous and is called clean line. A pure line is the offspring of one homozygous self-pollinated individual. Since mutation processes are constantly occurring, there are practically no absolutely homozygous individuals in nature.

Natural selection. This type of selection plays a decisive role in selection. A complex of factors acts on any plant during its life. environment, and it must be resistant to pests and diseases, adapted to a certain temperature and water regime.

Hybridization- the process of formation or production of hybrids, which is based on the combination of the genetic material of different cells in one cell. It can be carried out within the same species (intraspecific hybridization) and between different systematic groups (distant hybridization, in which different genomes are combined). The first generation of hybrids is often characterized by heterosis, which is expressed in better adaptability, greater fecundity and viability of organisms. With distant hybridization, hybrids are often sterile. Most common in plant breeding method of hybridization of forms or varieties within the same species. Most modern varieties of agricultural plants have been created using this method.

distant hybridization- a more complex and time-consuming method of obtaining hybrids. The main obstacle to obtaining distant hybrids is the incompatibility of germ cells of crossed pairs and the sterility of hybrids of the first and subsequent generations. Distant hybridization is the crossing of plants belonging to different species. Distant hybrids are usually sterile, as they are disturbed meiosis(two haploid sets of chromosomes from different species cannot conjugate) and therefore no gametes are formed.

heterosis("hybrid strength") - a phenomenon in which hybrids surpass parental forms in a number of characteristics and properties. Heterosis is typical for hybrids of the first generation, the first hybrid generation gives an increase in yield up to 30%. In subsequent generations, its effect weakens and disappears. The effect of heterosis is explained by two main hypotheses. Dominance hypothesis suggests that the effect of heterosis depends on the number of dominant genes in the homozygous or heterozygous state. The more genes in the genotype in the dominant state, the greater the effect of heterosis.

	♀AAbbCCdd		♂aaBBccDD
	AaBbCcDd

Overdominance hypothesis explains the phenomenon of heterosis by the effect of overdominance. overdominance- a type of interaction of allelic genes, in which heterozygotes are superior in their characteristics (in weight and productivity) to the corresponding homozygotes. Starting from the second generation, heterosis fades, as part of the genes passes into the homozygous state.

cross pollination self-pollinators makes it possible to combine the properties of different varieties. For example, when breeding wheat, proceed as follows. Anthers are removed from the flowers of a plant of one variety, a plant of another variety is placed next to it in a vessel with water, and plants of two varieties are covered with a common insulator. As a result, hybrid seeds are obtained that combine the traits of different varieties that the breeder needs.

Method for obtaining polyploids. Polyploid plants have a larger mass of vegetative organs, larger fruits and seeds. Many crops are natural polyploids: wheat, potatoes, varieties of polyploid buckwheat, sugar beets have been bred. Species in which the same genome is multiply multiplied are called autopolyploids. The classic method for obtaining polyploids is the treatment of seedlings with colchicine. This substance blocks the formation of spindle microtubules during mitosis, the number of chromosomes doubles in the cells, and the cells become tetraploid.

Use of somatic mutations. Somatic mutations are used to select vegetatively propagating plants. This was used in his work by I.V. Michurin. By vegetative propagation, a beneficial somatic mutation can be maintained. In addition, only with the help of vegetative propagation, the properties of many varieties of fruit and berry crops are preserved.

experimental mutagenesis. It is based on the discovery of the impact of various radiations to obtain mutations and on the use of chemical mutagens. Mutagens allow you to get large spectrum various mutations. Now more than a thousand varieties have been created in the world, leading a pedigree from individual mutant plants obtained after exposure to mutagens.

Plant breeding methods proposed by I.V. Michurin. Using the method of mentor I.V. Michurin sought to change the properties of the hybrid in the right direction. For example, if it was necessary to improve the taste of a hybrid, cuttings from a parent organism that had good taste were grafted into its crown, or a hybrid plant was grafted onto a rootstock, in the direction of which it was necessary to change the quality of the hybrid. I.V. Michurin pointed to the possibility of controlling the dominance of certain traits during the development of a hybrid. For this, in the early stages of development, it is necessary to influence certain external factors. For example, if hybrids are grown in open ground, their frost resistance increases on poor soils.