GENETICS - THEORETICAL BASIS OF SELECTION. SELECTION AND ITS METHODS.

• Breeding is the science of breeding new and improving existing old varieties of plants, animal breeds and strains of microorganisms with properties necessary for humans.
• A variety is a population of plants artificially created by man, which is characterized by a certain gene pool, hereditarily fixed morphological and physiological characteristics, a certain level and nature of productivity.
• A breed is a population of animals artificially created by man, which is characterized by a certain gene pool, hereditarily fixed morphological and physiological characteristics, a certain level and nature of productivity.
• Strain - a population of microorganisms, artificially created by man, which is characterized by a certain gene pool, hereditarily fixed morphological and physiological characteristics, a certain level and nature of productivity.

2. What are the main tasks of breeding as a science?

1. Increasing the productivity of plant varieties, animal breeds and strains of microorganisms;
2. Studying the diversity of plant varieties, animal breeds and strains of microorganisms;
3. Analysis of the laws of hereditary variability during hybridization and mutation process;
4. Study of the role of the environment in the development of signs and properties of organisms;
5. Development of artificial selection systems that contribute to the strengthening and consolidation of traits useful for humans in organisms with different types of reproduction;
6. Creation of varieties and breeds resistant to diseases and climatic conditions;
7. Obtaining varieties, breeds and strains suitable for mechanized industrial cultivation and breeding.

3. What is the theoretical basis of selection?

Answer: The theoretical basis of selection is genetics. It also uses the achievements of the theory of evolution, molecular biology, biochemistry and other biological sciences.

4. Complete the table "selection methods".

5. What is the importance of selection in human economic activity?

Answer: Breeding allows you to increase the productivity of plant varieties, animal breeds and strains of microorganisms; to develop systems of artificial selection that contribute to the strengthening and consolidation of traits useful for humans in various organisms; to create varieties and breeds resistant to diseases and climatic conditions; to obtain varieties, breeds and strains suitable for mechanized industrial cultivation and breeding.

TEACHING N.I. VAVILOV ON CENTERS OF DIVERSITY AND ORIGIN OF CULTURAL PLANTS.

1. Give definitions of concepts.

• The center of diversity and origin is the territory (geographical area) within which a species or other systematic category of agricultural crops was formed and from where they spread.
• Homologous series - a similar series of hereditary variability in genetically close species and genera.

2. Formulate the law of homologous series of hereditary variability.

Answer: Species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity that, knowing the number of forms within one species, one can foresee the finding of parallel forms in other species and genera. The closer genera and species are genetically located in the general system, the more complete is the similarity in the series of their variability. 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.

3. Fill in the table " Centers of origin and diversity of cultivated plants.

BIOTECHNOLOGY, ITS ACHIEVEMENTS AND DEVELOPMENT PROSPECTS.

1. Give definitions of concepts.

• Biotechnology is a discipline that studies the possibilities of using living organisms, their systems or products of their vital activity to solve technological problems, as well as the possibility of creating living organisms with the necessary properties by genetic engineering.
• Cellular engineering is the creation of a new type of cells based on their hybridization, reconstruction and cultivation. In the narrow sense of the word, this term is understood as the hybridization of protoplasts or animal cells, in the broad sense - various manipulations with them aimed at solving scientific and practical problems.
• Genetic engineering is a set of techniques, methods and technologies for obtaining recombinant RNA and DNA, isolating genes from an organism, manipulating genes and introducing them into other organisms.

2. What is the role of biotechnology in human practice?

Answer: Biotechnology processes are used in bakery, winemaking, brewing, fermented milk products; microbiological processes - to obtain acetone, butanol, antibiotics, vitamins, feed protein; biotechnology also includes the use of living organisms, their systems or products of their vital activity to solve technological problems, the possibility of creating living organisms with the necessary properties.

3. What are the prospects for the development of biotechnology?

Further development of biotechnology will help solve a number of important tasks:

1. Solve the food shortage problem.
2. Increase the yield of cultivated plants, create varieties that are more resistant to adverse effects, and also find new ways to protect plants.
3. Create new biological fertilizers, biohumus.
4. Find alternative sources of animal protein.
5. Propagate plants vegetatively using the tissue culture method.
6. Create new drugs and dietary supplements.
7. Conduct early diagnosis of infectious diseases and malignant neoplasms.
8. Obtain environmentally friendly fuels by recycling industrial and agricultural waste.
9. Recycle minerals in new ways.
10. Use biotechnology methods in most industries for the benefit of humanity.

4. What do you see as possible negative consequences of uncontrolled research in the field of biotechnology?

Answer: Transgenic products can harm health, cause malignant tumors. Human cloning is inhumane and contrary to the worldviews of many nations. The latest developments in biotechnology can lead to uncontrolled consequences: the creation of new viruses and microorganisms that are extremely dangerous for humans, as well as to controlled ones: the creation of biological weapons.

Genetics is the theoretical basis of selection. All modern breeding methods rely on the use of genetic principles. The provisions of genetics on the discrete nature of heredity, the doctrine of mutational and modification variability, the establishment of patterns of splitting of traits, the concepts of dominance and recessiveness, homo- and heterozygosity, and others form the basis of breeding work at the present time.

Already in the first period of its development, genetics made an important contribution to the theory of selection. The work of N. I. Vavilov and I. V. Michurin was of outstanding importance for the development of genetic methods of plant breeding.

N. I. Vavilov discovered the law of homological series in hereditary variability, created the doctrine of the world centers of origin of cultivated plants, and laid the genetic and breeding foundations of the doctrine of plant immunity to diseases and pests.

I. V. Michurin was the first among biologists to put forward the position on the possibility of controlling the process of creating forms and varieties with the characteristics and properties that a person needs. Having substantiated this position theoretically, he brought out a large number of varieties of fruit and berry plants. I. V. Michurin developed the theory of distant hybridization and the doctrine of dominance control for the formation of traits and properties of perennial plants in the process of ontogenesis.

Initially, selection was based on artificial selection, when a person selects plants or animals with traits of interest to him. Until the 16th-17th centuries, 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 is used, crossing plants with desirable traits and subsequently selecting from the offspring those individuals in which the beneficial properties are most pronounced. For example, one variety of wheat has a strong stem and is resistant to lodging, while a variety with a thin straw is not infected with stem rust. When plants from two varieties are crossed, different combinations of traits appear in the offspring. But it is precisely those plants that are selected that simultaneously have a strong straw and do not suffer from stem rust. This is how a new variety is created.

The main methods of breeding in general and plant breeding in particular are selection and hybridization. For cross-pollinated plants, mass selection of individuals with the desired properties is used. Otherwise, it is impossible to obtain material for further crossing. In this way, for example, new varieties of rye are obtained. These varieties are not genetically homogeneous. If it is desirable to obtain a pure line - that is, a genetically homogeneous variety, then individual selection is used, in which, by self-pollination, offspring are obtained from a single individual with desirable traits. Many varieties of wheat, cabbage, etc. were obtained by this method.

To consolidate useful hereditary properties, it is necessary to increase the homozygosity of a new variety. Sometimes self-pollination of cross-pollinated plants is used for this. In this case, the adverse effects of recessive genes may be phenotypically manifested. The main reason for this is the transition of many genes to the homozygous state. In any organism, unfavorable mutant genes gradually accumulate in the genotype. They are most often recessive and do not appear phenotypically. But when they self-pollinate, they go into a homozygous state, and an unfavorable hereditary change occurs. In nature, in self-pollinated plants, recessive mutant genes quickly pass into a homozygous state, and such plants die, being culled by natural selection.

Despite the adverse effects of self-pollination, it is often used in cross-pollinated plants to obtain homozygous ("pure") lines with the desired traits. This leads to a decrease in yield. However, then cross-pollination is carried out between different self-pollinating lines and as a result, in some cases, high-yielding hybrids are obtained that have the properties desired by the breeder. This is a method of interline hybridization, in which the effect of heterosis is often observed: hybrids of the first generation have a high yield and resistance to adverse effects. Heterosis is typical for hybrids of the first generation, which are obtained by crossing not only different lines, but also different varieties and even species. The effect of heterozygous (or hybrid) power is strong only in the first hybrid generation, and gradually decreases in subsequent generations. The main cause of heterosis is the elimination of the harmful manifestation of accumulated recessive genes in hybrids. Another reason is the combination of dominant genes of parental individuals in hybrids and the mutual enhancement of their effects.

In plant breeding, experimental polyploidy is widely used, since polyploids are characterized by rapid growth, large size and high yield. In agricultural practice, triploid sugar beet, four-ploid clover, rye and durum wheat, as well as six-ploid soft wheat are widely used. Artificial polyploids are obtained using chemicals that destroy the spindle of division, as a result of which the duplicated chromosomes cannot disperse, remaining in one nucleus. One such substance is colchicine. The use of colchicine to produce artificial polyploids is one example of artificial mutagenesis used in plant breeding.

By means of artificial mutagenesis and subsequent selection of mutants, new high-yielding varieties of barley and wheat were obtained. Using the same methods, it was possible to obtain new strains of fungi that produce 20 times more antibiotics than the original forms. Now more than 250 varieties of agricultural plants are cultivated in the world, created using physical and chemical mutagenesis. These are varieties of corn, barley, soybeans, rice, tomatoes, sunflower, cotton, ornamental plants.

When creating new varieties using artificial mutagenesis, researchers use the law of homologous series of N. I. Vavilov. An organism that has received new properties as a result of a mutation is called a mutant. Most mutants have reduced viability and are weeded out in the process of natural selection. For the evolution or selection of new breeds and varieties, those rare individuals that have favorable or neutral mutations are needed.

One of the achievements of modern genetics and breeding is overcoming the infertility of interspecific hybrids. For the first time, G.D. Karpechenko managed to do this when obtaining a cabbage-radish hybrid. As a result of distant hybridization, a new cultivated plant was obtained - triticale - a hybrid of wheat and rye. Remote hybridization is widely used in fruit growing.

The basic principles of animal breeding are no different from the principles of plant breeding. However, the selection of animals has some features: they are characterized only by sexual reproduction; mostly very rare alternation of generations (in most animals after a few years); the number of individuals in the offspring is small. Therefore, in breeding work with animals, it is important to analyze the totality of external features, or exterior, characteristic of a particular breed.

One of the most important achievements of man at the dawn of his formation and development (10-12 thousand years ago) was the creation of a constant and fairly reliable source of food by domesticating wild animals. The main factor in domestication is the artificial selection of organisms that meet human requirements. Domestic animals have highly developed individual traits, often useless or even harmful to their existence in natural conditions, but useful to humans. For example, the ability of some breeds of chickens to produce more than 300 eggs per year is devoid of biological meaning, since a chicken will not be able to incubate such a number of eggs. Therefore, under natural conditions, domesticated forms cannot exist.

Domestication led to a weakening of the effect of stabilizing selection, which sharply increased the level of variability and expanded its range. At the same time, domestication was accompanied by selection, at first unconscious (the selection of those individuals that looked better, had a calmer disposition, possessed other qualities valuable to humans), then conscious, or methodical. The widespread use of methodical selection is aimed at the formation in animals of certain qualities that satisfy humans.

The process of domestication of new animals to meet human needs continues in our time. For example, in order to obtain fashionable and high-quality furs, a new branch of animal husbandry has been created - fur farming.

The selection of parental forms and types of crossing of animals are carried out taking into account the goal set by the breeder. This can be a purposeful obtaining of a certain exterior, an increase in milk production, milk fat content, meat quality, etc. Breeding animals are evaluated not only by external signs, but also by the origin and quality of offspring. Therefore, it is necessary to know their pedigree well. In breeding farms, when selecting producers, a record of pedigrees is always kept, in which the exterior features and productivity of parental forms are evaluated over a number of generations. According to the traits of the ancestors, especially on the maternal line, one can judge with a certain probability about the genotype of the producers.

In breeding work with animals, two methods of crossing are mainly used: outbreeding and inbreeding.

Outbreeding, or unrelated crossing between individuals of the same breed or different breeds of animals, with further strict selection, leads to the maintenance of useful qualities and to their strengthening in the next generations.

When inbreeding, brothers and sisters or parents and offspring (father-daughter, mother-son, cousins, etc.) are used as initial forms. Such crossing is to a certain extent similar to self-pollination in plants, which also leads to an increase in homozygosity and, as a result, to the consolidation of economically valuable traits in the offspring. At the same time, homozygotization for the genes that control the studied trait occurs the faster, the more closely related crossing is used for inbreeding. However, homozygotization during inbreeding, as in the case of plants, leads to the weakening of animals, reduces their resistance to environmental influences, and increases the incidence. To avoid this, it is necessary to carry out a strict selection of individuals with valuable economic traits.

In breeding, inbreeding is usually only one step in improving a breed. This is followed by crossing different interline hybrids, as a result of which unwanted recessive alleles are transferred to a heterozygous state and the harmful effects of inbreeding are markedly reduced.

In domestic animals, as well as in plants, the phenomenon of heterosis is observed: during interbreeding or interspecific crosses, hybrids of the first generation experience especially powerful development and an increase in viability. A classic example of the manifestation of heterosis is the mule - a hybrid of a mare and a donkey. This is a strong, hardy animal that can be used in much more difficult conditions than the parental forms.

Heterosis is widely used in industrial poultry farming (for example, broiler chickens) and pig breeding, since the first generation of hybrids is directly used for economic purposes.

distant hybridization. Distant hybridization of domestic animals is less efficient than that of plants. Interspecific hybrids of animals are often sterile. At the same time, the restoration of fertility in animals is a more difficult task, since it is impossible to obtain polyploids based on the multiplication of the number of chromosomes in them. True, in some cases, distant hybridization is accompanied by normal fusion of gametes, normal meiosis and further development of the embryo, which made it possible to obtain some breeds that combine valuable features of both species used in hybridization. For example, in Kazakhstan, based on the hybridization of fine-fleeced sheep with wild mountain sheep argali, a new breed of fine-fleeced argali merinos has been created, which, like argali, graze on high mountain pastures that are inaccessible to fine-fleeced merinos. Improved breeds of local cattle.

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 consumer qualities of products.

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

Reducing the share of losses from pests and diseases.

The teachings of N.I. Vavilov about the centers of 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 (initially, N.I. Vavilov identified 8 centers, but then reduced their number to 7). 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, sugar cane, tea, lemon, orange, banana, eggplant, as well as a large number of 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.

About 15% of the world's cultural flora originates from this territory. Wild relatives of wheat, rye and various European fruits are concentrated here in exceptional species diversity. Until now, it is possible to trace here for many species a continuous series from cultivated to wild forms, that is, to establish preserved connections between wild forms and cultivated ones.

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

5. Abyssinian center. The total number of cultivated plant species 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 coffee tree, watermelon, teff cereal (Eragrostis abyssinica), nougat oil plant (Guizolia ahyssinica), a special kind of banana.

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 the vast territory of 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.

Law of homologous series

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. The closer genera and species are genetically located in the general system, the more complete is the similarity in the series of their variability.

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

Selection is the science of methods for creating highly productive plant varieties, animal breeds and strains of microorganisms.

Modern selection is a vast area of ​​human activity, which is a fusion of various branches of science, the production of agricultural products and their complex processing.

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 consumer qualities of products.

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

Reducing the share of losses from pests and diseases.

Theoretical basis of selection is genetics, since it is the knowledge of the laws of genetics that makes it possible to purposefully control the appearance of mutations, predict the results of crossing, and correctly select hybrids. As a result of applying the knowledge of genetics, it was possible to create more than 10,000 varieties of wheat based on several original wild varieties, to obtain new strains of microorganisms that secrete food proteins, medicinal substances, vitamins, etc.

Selection Methods the main specific methods of selection remain hybridization and artificial selection.Hybridization

Crossing organisms with different genotypes is the main method for obtaining new combinations of traits.

There are the following types of crosses:

Intraspecific crossbreeding- different forms are crossed within a species (not necessarily varieties and breeds). Intraspecific crossings also include crossings of organisms of the same species living in different environmental conditions.

closely related crosses induction 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). Backcrosses (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- these are crossings of dominant forms with an unknown genotype and recessive-homozygous tester lines.

distant crossbreeding- interspecific and intergeneric. Usually distant hybrids are sterile and are propagated vegetatively.

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.

Mass selection- The entire group is selected. 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 (including long-term modifications). Used in seed production. The advantage of this form of selection is the preservation of a high level of genetic diversity in the selected group of plants.

Individual selection- individual individuals are selected, and the seeds collected from them are sown separately. Individual selection is considered to be a progressive form of selection because it eliminates the effect of modification variability.

A type of family selection is sib selection . The basis of sib-selection is selection for the closest relatives (siblings - brothers and sisters). A special case of sib-selection is the selection of sunflower for oil content halves method. When using this method, the inflorescence (basket) of sunflower is divided in half. The seeds of one half are checked for oil content: if the oil content is high, then the second half of the seeds are used in further selection.

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 of educational 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 Ch. Darwin, experimental studies of 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 a general definition of breeding as a science, N. I. Vavilov wrote: “Selection is essentially human intervention in the shaping of animals and plants; in other words, selection is an evolution directed by the will of man "N. I. Vavilov emphasized the high degree of complexity of selection 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 branches of practical application of 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 of 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

WHAT IS SELECTION.

The word "selection" comes from lat. "selectio", which in translation means "choice, selection". Breeding is a science that develops new ways and methods for obtaining plant varieties and their hybrids, animal breeds. It is also a branch of agriculture that is engaged in breeding new varieties and breeds with the properties necessary for humans: high productivity, certain product qualities, resistant to diseases, well adapted to certain growth conditions.

GENETICS AS A THEORETICAL BASIS OF SELECTION.

The theoretical basis of selection is genetics - the science of the laws of heredity and variability of organisms and methods of managing them. She studies the patterns of inheritance of characteristics and properties of parental forms, develops methods and techniques for managing heredity. Applying them in practice when breeding new varieties of plants and animal breeds, a person receives the necessary forms of organisms, and also controls their individual development by montogenesis. The foundations of modern genetics were laid by the Czech scientist G. Mendel, who in 1865 established the principle of discreteness, or discontinuity, of the inheritance of signs and properties of organisms. In experiments with peas, the researcher showed that the characteristics of parental plants are not destroyed or mixed during crossing, but are transmitted to offspring either in a form characteristic of one of the parents, or in an intermediate form, reappearing in subsequent generations in certain quantitative ratios. His experiments also proved that there are material carriers of heredity, later called genes. They are specific to each organism. At the beginning of the twentieth century, the American biologist T. H. Morgan substantiated the chromosome theory of heredity, according to which hereditary traits are determined by chromosomes - the organelles of the nucleus of all body cells. The scientist proved that the genes are located linearly among the chromosomes and that the genes of one chromosome are linked to each other. A trait is usually determined by a pair of chromosomes. During the formation of germ cells, paired chromosomes diverge. Their full set is restored in a fertilized cell. Thus, a new organism receives chromosomes from both parents, and with them inherits certain traits. In the 1920s, mutational and population genetics arose and began to develop. Population genetics is a field of genetics that studies the main factors of evolution - heredity, variability and selection - in specific environmental conditions, populations. The founder of this direction was the Soviet scientist S. S. Chetverikov. We will consider mutational genetics in parallel with mutagenesis. In the 1930s, the geneticist N. K. Koltsov suggested that chromosomes are giant molecules, thereby anticipating the emergence of a new direction in science - molecular genetics. Later it was proved that chromosomes consist of protein and molecules of deoxyribonucleic acid (DNA). DNA molecules contain hereditary information, a program for the synthesis of proteins, which are the basis of life on Earth. Modern genetics is developing comprehensively. It has many directions. Allocate the genetics of microorganisms, plants, animals and humans. Genetics is closely related to other biological sciences - evolutionary theory, molecular biology, biochemistry. It is the theoretical basis of selection. On the basis of genetic studies, methods have been developed for obtaining hybrids of corn, sunflower, sugar beet, cucumber, as well as hybrids and crossbreeds of animals with heterosis due to (heterosis is the acceleration of growth, increase in size, increase in the viability and productivity of hybrids of the first generation compared to parental organisms ) increased productivity.