Selection is the science of creation methods. Breed, variety, strain are populations of organisms obtained in

Selection is the science of improving individual qualities of animals and plants, necessary for a person, as well as the development of new plant varieties, animal breeds, and strains of microorganisms. Plant breeding methods are used to create cultivated varieties.

Selection

Most of the plants that modern humanity eats are the product of selection (potatoes, tomatoes, corn, wheat). For several centuries, people cultivated wild plants, moving from gathering to farming.

The selection directions are:

high productivity;
plant nutrition (for example, protein content in wheat);
improved taste;
resistance of crops to weather conditions;
early ripening of fruits;
intensity of development (for example, “responsiveness” to fertilizers or watering).

Rice. 1. Comparison of wild and agricultural corn.

Selection has solved problems with food shortages and continues to develop, introducing genetic engineering methods. Breeders not only improve the taste and nutritional value of plants, but also make them healthy, rich in vitamins and chemical elements important for metabolism.

For successful selection, it is necessary to understand the patterns of inheritance of traits, the particular influence of the environment, the morphological structure and methods of reproduction of cultivated plants.

Methods

The main selection methods are:

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artificial selection- human selection of the most valuable crops for breeding;
hybridization- the process of obtaining offspring from crossing different genetic forms;
artificial mutagenesis- making changes to DNA.

Artificial selection includes two types - individual (by genotype) and mass (by phenotype).

In the first case, the specific qualities of plants are important, in the second, the most adapted individuals are selected.

There are two types of hybridization:

intraspecific or closely related - inbreeding;
distant (interspecific) - outbreeding.

Classical plant breeding methods are described in the table.

*Method*	*The essence*	*Examples*
Individual selection	Carry out in relation to self-pollinating plants. Breeding single individuals with the desired qualities and obtaining improved offspring from them	Wheat, barley, peas
Mass selection	Carry out in relation to cross-pollinated plants. Plants are crossed en masse. The best specimens are selected from the resulting offspring and crossed again. Can be repeated until they are withdrawn necessary qualities plants	Sunflower
Inbreeding	Occurs when self-pollination of cross-pollinated plants occurs. As a result, pure (homozygous) lines are obtained to consolidate the resulting trait. There is a decrease in viability (inbreeding depression), because offspring gradually transition to a homozygous recessive state	Varieties of pears and apple trees
Outbreeding	Different species are crossed, the descendants are usually sterile, because When crossing, meiosis is disrupted and gametes are not formed. In the first generation, the effect of heterosis is observed - the superiority of descendants over parental forms due to the formation of heterozygous genes. The more distant the parents are in relationship, the more clearly heterosis manifests itself.	Hybrids of wheat and rye (triticale), currants and gooseberries (yoshta)
Mutagenesis	Plants are exposed to ionizing, laser radiation, chemical or biological effects, resulting in mutations. Most often, resistance to diseases and pests is developed in this way. The method has been improved by genetic engineering - the desired gene can be “turned on” or “turned off” manually without losing other useful characteristics	Wheat varieties

Rice. 2. Examples of hybrids.

Unsuccessful selection experience - Sosnovsky's hogweed. The plant was cultivated as livestock feed. However, it later turned out that the new hogweed easily penetrates ecosystems, displacing natural plants, and also contains substances that increase sensitivity to ultraviolet radiation. Once on the skin, the juice causes sunburn.

Rice. 3. Sosnovsky's hogweed.

What have we learned?

From the lesson we learned about why selection is necessary and what methods are used in plant breeding. We considered classical selection methods - individual and mass selection, intraspecific and distant hybridization, mutagenesis.

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Question 1. What is selection?
Selection is the science of creating new and improving existing varieties of plants, animal breeds and strains of microorganisms. At the same time, selection is the process of creating varieties, breeds and strains. The theoretical basis of selection is genetics. Thanks to the selection of approximately 150 species of cultivated plants and 20 species of domesticated animals, thousands of different varieties have been created. different breeds and varieties. Selection has replaced spontaneous, everyday methods for keeping and breeding plants and animals that people have used for thousands of years.
Breeders study the specific patterns of evolution of domestic animals and cultivated plants, which occurs under the directing influence of humans.

Question 2. What is called a breed, variety, strain?
A breed, variety or strain is a collection of individuals of the same species, artificially created by man and characterized by certain hereditary properties. All organisms of this set have a set of genetically fixed morphological and physiological characteristics. This means that all key genes are transferred to a homozygous state and splitting does not occur in a number of generations. Breeds, varieties and strains are able to maximize their beneficial qualities for humans only in the conditions for which they were created.

Question 3. What basic selection methods do you know?
The main methods of selection are selection and hybridization.
Selection- this is the selection of individuals with certain characteristics in each generation for the purpose of their subsequent crossing. Selection is usually carried out over several successive generations. There is a distinction between mass and individual selection.
Hybridization- this is the directed crossing of certain individuals to obtain new or consolidate the necessary characteristics with the aim of breeding a breed (variety) that does not yet exist or preserving the properties of an already existing set of individuals. Hybridization can be intraspecific and interspecific (distant).

Question 4. What is mass selection, individual selection?
Mass selection is carried out on phenotypic traits and is usually used in crop production when working with cross-pollinating plants. If the necessary characteristics of the population (for example, seed weight) have improved, then we can assume that mass selection on the phenotype was effective. It is in this way that many varieties of cultivated plants were created. In the case of selection of microorganisms, only mass selection can be used.
With individual selection, individual individuals are selected, and the offspring of each of them is studied and monitored over several generations. This makes it possible to determine the genotypes of individuals and use for further selection those organisms that have the optimal combination of traits and properties useful to humans. As a result, varieties and breeds are obtained with high homogeneity and constancy of characteristics, since all individuals included in them are descendants of a small number of parents. For example, some cat breeds and varieties of ornamental plants are the result of the persistence of a single mutation (i.e., the altered genotype of one ancestor individual).

Question 5. What difficulties arise when performing interspecific crosses?
Interspecific crossing is possible only for biologically close species (horse and donkey, ferret and mink, lion and tiger). However, even in this case, hybrids, although characterized by heterosis (i.e., superior in properties to their parents), often turn out to be infertile or low in fertility. The reason for this is the impossibility of conjugation of chromosomes of different biological species, as a result of which meiosis is disrupted and gametes are not formed. To solve this problem, various techniques are used. In particular, in order to obtain a fertile hybrid of cabbage and radish, breeder G. D. Karpechenko used the polyploidization method. He crossed not diploid, but tetraploid plants. As a result, in the first prophase of meiosis (prophase I), chromosomes belonging to the same species could form bivalents. The division proceeded normally, and full-fledged gametes were formed. This experiment became an important stage in the development of selection.

“Biology selection” - On the website of the gymnasium, view the presentations of students of grade 10 B on the topic “Directions of biotechnology.” Centers of origin of cultivated plants. Exposure to radiation and chemicals on plants and animals. Selection tasks. Hybridization method. Mutagenesis method. Selection method. Selection methods. Homework.

“Basic selection methods” - Heterotic animals are distinguished by early maturity and increased meat productivity. 10. Brewing. 8. Polyploidy is extremely rare in animals. 7. 4. Use of the heterosis effect. Preparation of many dairy products. Selection.

“Plant breeding” - Kudoyarova G.R. Laboratory of Plant Physiology, Institute of Biology. A correlation was found between plant productivity under moderate drought conditions and relative water content (WWC, left) and ABA content (right) RWC=(wet weight - dry weight)/(turgor weight - dry weight). Productivity of Mexican corn varieties.

“Selection in biotechnology” - What do we know about the use of microorganisms? Root cancer of fruit crops. Sterlet. A mule is the result of crossing a donkey and a mare. In total there are more than 300 varieties of different plants! Beltyukova K.I.). Kyiv: Naukova Dumka, 1966. A.A. Kamensky, E.A.Kriksunov, V.V.Pasechnik General biology 10-11th grade Ed. "Bustard" 2006

“Methods of selection of animals and plants” - Methods of selection of plants and animals. Selection methods: selection, hybridization, mutagenesis. Biotechnology. Municipal educational institution Bazhenovskaya secondary comprehensive school. Selection of microorganisms. Sometimes viruses are classified as microorganisms. Presentation on biology on the topic: Completed by: Cormina Irina, 10th grade student.

“Vavilov fundamentals of selection” - Lesson structure. Method of organization educational process based on block-modular representation educational information. Works by N.I. Vavilov. modular block "Selection". Complex didactic goal (CDT): Biology teacher of Municipal Educational Institution Lyceum No. 11 Volkova M.P. Basics of selection.

There are a total of 26 presentations in the topic

Selection - the science of creating new and improving existing varieties of plants, animal breeds and strains of microorganisms. The scientific foundations of selection were laid by Charles Darwin in his work “The Origin of Species” (1859), where he illuminated the causes and nature of the variability of organisms and showed the role of selection in the creation of new forms. An important step Further development of selection was the discovery of the laws of heredity. M. made a great contribution to the development of selection. I. Vavilov, author of the law of homological series in hereditary variability and the theory of the centers of origin of cultivated plants.

Subject of selection is the study in man-made conditions of the patterns of change, development, transformation of plants, animals and microorganisms. With the help of selection, methods of influencing cultivated plants and domestic animals are being developed. This happens with the aim of changing their hereditary qualities in the direction necessary for a person. Selection has become one of the forms of evolution of the plant and animal world. It is subject to the same laws as the evolution of species in nature, however natural selection here partially replaced by artificial.

Theoretical basis of selection is genetics, evolutionary doctrine. Using evolutionary theory, laws of heredity and variability, the doctrine of pure lines and mutations, breeding scientists have developed various methods for breeding plant varieties, animal breeds and strains of microorganisms. The main selection methods include selection, hybridization, polyploidy, experimental mutagenesis, genetic engineering methods, etc.

The main tasks of modern selection is to increase the productivity of varieties and breeds, transfer them to an industrial basis, create breeds, varieties and strains adapted to the conditions of modern Agriculture, ensuring full production food products at the lowest cost, etc.

There are three main sections in breeding: plant breeding, animal breeding and microbial breeding.

The concept of breed, variety, strain

The objects and end result of the selection process are breeds, varieties and strains.

Animal breed- this is a collection of individuals within a certain species of animal, as if it has genetically determined stable characteristics (properties and signs) , distinguishing it from other sets of individuals of this species of animals, are steadily transmitted to their descendants and are the result of human intellectual activity. Animals of the same breed are similar in body type, productivity, fertility, color. This allows you to distinguish them from other breeds. There must be a sufficient number of animals in the breed, otherwise the possibility of applying selection is limited, quickly leading to forced inbreeding and, as a consequence, to the degeneration of the breed. In addition to high productivity and numbers, the breed must be quite common. This increases the possibilities for creating in it various types, which contributes to its further improvement. Natural geographical conditions have a great influence on the formation of rock characteristics - characteristics of soils, plants, climate, terrain, etc. When animals are brought into new natural and climatic conditions, physiological changes occur in their bodies, and in some cases they are profound, in others they are profound. The restructuring of the body's systems is deeper, the greater the difference between the new and previous conditions of existence. The process of animals adapting to new living conditions is called acclimatization; it can last several generations.

Plant variety - a group of cultivated plants that, as a result of selection, have received a certain set of characteristics (useful or decorative) , which distinguish this group of plants from other plants of the same species. Each plant variety has a unique name and retains its properties after repeated cultivation.

Microorganism strain - a pure culture of a certain type of microorganism, the morphological and physiological characteristics of which have been well studied. Strains can be isolated from different sources (soil, water, food) or from the same source at different times. Therefore, the same type of bacteria, yeast, microscopic fungi can have a large number of strains that differ in a number of properties, for example, sensitivity to antibiotics, the ability to form toxins, enzymes and other factors. Strains of microorganisms that are used in industry for the microbiological synthesis of proteins (in particular enzymes), antibiotics, vitamins, organic acids, etc., are much more productive (as a result of selection) than wild strains.

Breeds, varieties, strains are not capable of existing without constant attention person. Each variety, breed, strain is characterized by a certain reaction to conditions environment. This means that they positive traits can manifest themselves only at a certain intensity of environmental factors. Scientists in scientific and practical institutions comprehensively study the properties of new breeds and varieties and check their suitability for use in a certain climatic zone, that is, they carry out their zoning. Zoning niya - a set of measures aimed at checking the conformity of the qualities of certain breeds or varieties to the conditions of a certain natural zone, which is a necessary condition their rational use on the territory of any country. The best for use in a certain climate zone are zoned varieties, breeds, the positive properties of which can only appear under certain conditions.

Biology. General biology. Grade 10. A basic level of Sivoglazov Vladislav Ivanovich

32. Selection: basic methods and achievements

Remember!

What is selection?

Give examples of animal breeds and plant varieties known to you.

More than 10 thousand years ago, humanity switched to a sedentary lifestyle and found itself completely dependent on a limited number of plant and animal species, which it could use as its food and economic resources. An urgent need has arisen to improve the quality of cultivated plants and domestic animals, that is, to engage in breeding. Selection(from lat. selectio– selection) is the science of creating new and improving existing varieties of plants, animal breeds and strains of microorganisms. At the same time, selection is understood as the process of creating varieties, breeds and strains. The theoretical basis of selection is genetics.

Currently, out of the entire plant diversity, humans cultivate about 150 species as cultivated plants, and out of many tens of thousands of species of vertebrate animals, humans have domesticated only about 20.

Centers of origin of cultivated plants. The outstanding Russian geneticist and breeder Nikolai Ivanovich Vavilov made a great contribution to the study of the origin of cultivated plants. Having completed at the beginning of the 20th century. more than 60 expeditions around the world, Vavilov and his colleagues discovered that the greatest variety of varieties of one or another is concentrated in certain areas of the globe cultivated plant. For example, for potatoes, the maximum genetic diversity is associated with South America, the most varieties of rice were found in China and Japan, and the most varieties of corn were found in Mexico. After analyzing the results of his trips, Vavilov came to the conclusion that areas of maximum diversity are the centers of origin of a given culture and, as a rule, are associated with ancient centers of agricultural civilizations. Vavilov identified seven main such centers (Fig. 102).

During the expeditions, a unique collection of plant seeds was collected, which was subsequently constantly replenished and studied by employees of the All-Union Institute of Plant Growing in St. Petersburg, which now bears the name of N. I. Vavilov. Currently it has more than 300 thousand species, varieties and forms. When starting work on creating a new plant variety, a breeder can select from the available rich source material those samples that most fully possess the characteristics of interest to him.

Variety and breed. IN modern conditions development of society important has the intensification of agricultural production, i.e. obtaining the maximum amount of products at minimum costs. For this purpose, highly productive animal breeds and plant varieties are created that are resistant to extreme environmental conditions, diseases and pests, and have certain necessary qualities(Fig. 103). Breed, variety or strain is a collection of individuals of the same species, artificially created by man and characterized by certain hereditary properties. All organisms that make up such a set have similar, hereditarily fixed morphological and physiological properties and are capable of maximizing their qualities in the conditions for which they were created. The dachshund may be an excellent burrowing hunting dog, but it is pointless to use it as a hound. In the same way, a greyhound that easily overtakes a hare will be a poor guard compared to a German shepherd.

Rice. 102. Centers of origin of cultivated plant species (according to N. I. Vavilov)

Rice. 103. Breeds of cattle

By creating certain breeds of animals, we often condemn them to the need for constant coexistence with humans. A cow that produces 10 thousand liters of milk per year will die within a few days if it is not milked.

Basic selection methods. The main methods of selection are selection and hybridization.

Selection. Selection can be mass or individual. Mass selection is carried out according to external, phenotypic characteristics and, as a rule, is used in plant growing when working with cross-pollinating plants (rye, corn, sunflower, etc.). From a huge number of plants, a group of the best plants for certain plant properties is selected. Their seeds are sown the next year and the best plants are again selected from the resulting offspring, the seeds of which are sown in a new field. If the productivity and other characteristics of the population have improved, we can assume that mass selection for phenotype was effective. Many varieties of cultivated plants have been bred in this way.

Unlike mass individual selection Individuals are selected and the offspring of each is studied over a series of generations. This makes it possible to fairly accurately assess the genotype of each parent organism and select for further work those individuals that turn out to be the most optimal in terms of the combination of traits and properties useful to humans. Varieties and breeds obtained as a result of individual selection are distinguished by high homogeneity and constancy of characteristics (Fig. 104).

Hybridization. Along with selection, an important method of selection is hybridization (crossing).

Hybridization can be closely related, which allows rare genes to appear in a homozygous state and thereby reveal hidden recessive alleles, and unrelated, used to combine in one organism the characteristics of different varieties, breeds, and sometimes even species and genera.

Closely related hybridization (inbreeding) transfers most recessive alleles to a homozygous state, which is why they begin to appear in the phenotype. Any organism always contains recessive genes in a latent state in its genotype ( Aa). If among them there are genes that reduce viability, then repeated inbreeding, transferring these genes to a homozygous state, can lead to degeneration of the breed or variety. This pattern is also true for people who practice consanguineous marriages. There are many known families who married only close relatives, increasing the number of hereditary diseases with each generation. For example, the Spanish royal dynasty of the Habsburgs degenerated and died out. Of course, rare recessive alleles can also be useful, in which case their manifestation in a homozygous form can increase the vitality, endurance or other useful qualities of their owner. If this happens, then breeders deliberately use inbreeding in the new breed they are breeding, which allows them to preserve the discovered original or useful trait.

Unrelated hybridization (outbreeding) are divided into intraspecific and distant.

Rice. 104. Cultivated varieties of cabbage and their wild ancestor

At the core intraspecific hybridization lies the directed crossing of individuals with certain properties in order to obtain offspring with the maximum manifestation of these qualities. For example, one plant variety has high productivity, but is easily infected with fungal diseases, while another, having high resistance to diseases, produces much fewer seeds. By crossing these two varieties, it is possible to obtain various combinations of traits in the offspring, among which there will be highly productive and at the same time resistant to infection plants.

Rice. 105. Ligers - interspecific hybrids between a lion and a tigress - look like huge lions with blurry stripes. Female liger (left) and male liger (right)

Distant hybridization consists of crossing different types(Fig. 105). In plant growing, with the help of distant hybridization, a new grain crop has been created - triticale, a hybrid of rye and wheat. This crop combines many of the properties of wheat (high baking qualities) and rye (the ability to grow on poor sandy soils).

A classic example of interspecific hybrids in livestock breeding is a mule, obtained by crossing a donkey with a mare, which is significantly superior to its parents in endurance and performance. In Kazakhstan, by crossing wild mountain argali sheep with fine-wool sheep, the famous argali sheep breed was created.

However, the use of interspecific crosses has certain difficulties, because the resulting hybrids often turn out to be infertile (sterile) or low-fertility. The sterility of hybrids is associated with the absence of paired homologous chromosomes. This makes the conjugation process impossible. Therefore, meiosis cannot be completed and no germ cells are formed. The famous Russian scientist Georgy Dmitrievich Karpechenko (1899–1942) was the first to propose a method of restoring fertility in distant plant hybrids using the polyploidy method.

Rice. 106. Heterosis by the productivity of a hybrid (in the center) obtained by crossing two different lines of corn (side by side)

When crossing different breeds of animals or plant varieties, as well as during interspecific crossings in the first generation, the viability of hybrids increases and powerful development is observed. The phenomenon of superiority of hybrids in their properties of parental forms is called heterosis, or hybrid power(Fig. 106).

Often in plant growing, polyploid plants are obtained, which are characterized by larger sizes, high yields and more active synthesis of organic substances. Polyploid varieties of clover, sugar beets, rye, and buckwheat are widespread.

Currently, humanity uses about 10% of the total land surface for agricultural production. It is no longer possible to increase this share, because almost all reserves have been exhausted. Them higher value is acquired by the breeding work of scientists who, based on the basic laws of heredity and variability, create new highly productive breeds and varieties. In recent years, breeding has been actively introducing techniques and methods of genetic and cellular engineering into practice.

Review questions and assignments

1. What is selection?

2. What is called a breed, variety, strain?

3. What basic selection methods do you know?

4. Select criteria and compare mass and individual selection.

5. What difficulties arise when performing interspecific crosses?

6. Are interspecific hybrids produced and used in your region? Using additional sources information, find out which species are hybrids of organisms such as bester, honorik, hinny, raphanobrassica. What interest are they for agriculture?

Think! Do it!

1. What are the similarities and differences between plant and animal breeding methods?

2. Why do each region need its own plant varieties and animal breeds? What varieties and breeds are typical for your region? What are their features and advantages?

3. Of the wide variety of animal species living on Earth, humans have selected relatively few species for domestication. What do you think explains this?

4. Heterosis usually does not persist in subsequent generations and fades away. Why is this happening?

5. Why do you think ligers are born only in zoos and are not found in wildlife? Explain your point of view.

6. Do you think mass selection can be used when breeding animals? Prove your opinion.

7. Using additional literature and Internet resources, prepare a message or presentation about the history of selection from ancient times to the present.

8. Are there breeding stations or centers in your region? What research are they doing? What are their achievements? Together with your teacher, organize an excursion to such a station.

9. Organize an exhibition “Achievements in breeding work” dedicated to the activities of local breeding centers and stations, seed farms, and variety testing sites (group project).

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Refer to the electronic application. Study the material and complete the assignments.

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Artificial mutagenesis. To one of modern trends selection refers artificial mutagenesis As is known, spontaneous mutations in nature occur extremely rarely, and therefore the breeder has to wait a very long time, sometimes his whole life, until a plant with the desired mutation appears on his farm. But the mutation process can be significantly accelerated if factors that increase the frequency of mutations, i.e., mutagenic factors, are used. We have already talked about these factors, they may be different kinds electromagnetic radiation, temperature changes, or certain chemicals. As a result of the use of artificial mutagenesis, organisms with a wide variety of mutations can appear. Most of these mutations will turn out to be useless or harmful, but sometimes some may arise that are of practical interest to the breeder. In this case, mutant individuals can be crossed with each other, and as a result of numerous repeated crossings, a new variety or breed with new useful traits can be obtained. Particularly significant results using artificial mutagenesis are obtained in the selection of microorganisms.

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