Plant breeding methods. Breeding methods Plant breeding methods summary

Simultaneously with the development of the process of domestication of representatives of wild fauna. Initially, people used the method of so-called unconscious selection, choosing those individuals who got along better with humans, could be useful, had a more docile character, were obedient and, most importantly, could continue their race in captivity and reproduce.

Approximately 9 thousand years BC, man began to more carefully select certain useful qualities in animals, that is, the era of methodical selection began. It was then that the selection of plants and animals began to develop in a more familiar sense to us. But domestication, like the selection method, continues to this day. For example, it is worth noting such an industry as fur farming.

Features of animal selection

It is necessary to highlight the features of animal selection in comparison with plant breeding. Firstly, representatives of the fauna are able to reproduce only sexually, that is, heterozygous organisms have a large proportion in the population. Secondly, they have a longer period of sexual maturity. Mammals are capable of reproduction not immediately after birth, but several years later. The third feature is that fauna representatives have much fewer offspring than plants.

All these features have formed special selection methods that are not typical for representatives of the flora. Of course, the basic methods, which include hybridization and selection, have been preserved. But completely different methods have also appeared that are not applicable to plants.

Breeding methods

Inbreeding, or imbreeding, is carried out through the mating of individuals who are sisters and brothers or descendants and parents. As a result, the required trait can become homozygous. However, it should be noted that over time there is a loss or significant deterioration in the viability of the resulting individuals.

Interbreeding, or outbreeding, is necessary to consolidate the necessary characteristics of both breeds. Thanks to outbreeding, a huge number of valuable breeds were obtained, for example, the white steppe Ukrainian pig, obtained from crossing a white English boar with outbred Ukrainian pigs. As a result, animal selection made it possible to obtain a breed that is distinguished by greater mass, a higher content of fat and meat, and is also extremely unpretentious.

Distant hybridization involves crossing pairs that belong to different species. This method has a huge disadvantage: all offspring are infertile. But animal selection was able to overcome even this problem. A striking example of distant hybridization is the mule, which is a cross between a donkey and a mare. The mule has the great endurance of a donkey and the docile nature of a horse.

Another method is artificial insemination. It is used to obtain as many offspring as possible from a particular sire.

Another new and very interesting method is embryo transplantation. It is based on a rather complex medical operation, when the number of eggs in the desired female is increased through hormonal therapy. Then the eggs are fertilized, embryos are removed, which are placed with other animals that perform the role or frozen at a temperature of 273 ̊C. Then they can be stored for a long period of time to be able to use them in the future.

Thus, animal selection solves one of the most important problems of all humanity - the problem of finding food and food. Modern science allows us to create new species that are more satisfying. And science never stands still.

Following taming and domestication, people began to breed various breeds of animals. This process is called selection. In this article we will talk about methods of animal selection, their characteristics and significance.

Features of animal selection

The selection of domestic pets began about 12 thousand years ago.
This process has a number of features:

reproduction occurs only sexually;
quality assessment occurs based on offspring;
in some species the generation changes after a few years;
a small number of offspring.

Initially, the selection of animals occurred unconsciously, but later people began to purposefully select the best representatives of the species to obtain certain qualities of the breed. Selection, as a science, arose on the basis of analysis and the generalized experience of many generations in breeding new breeds.

The work of breeders has several directions:

A combination of endurance to the environmental conditions of the natural area and productivity;
Improving quality indicators (ratio of meat and fat, fat content, wool quality, etc.);
Breeds with intensive growth, which help save costs;
The ability to resist diseases.

The main methods of animal selection are hybridization and individual selection. The latter method is based mainly on external indicators. Crossing can be closely related (inbreeding) or unrelated (outbreeding). Closely related hybridization, as in plants, can lead to depression.

Rice. 1. Methods of animal selection.

In addition, there are the following types of selection:

Breeding within the breed - helps preserve and improve the breed. Its peculiarity is the culling of individuals that do not meet breed requirements and the selection of the best producers;
Interbreed hybridization - used to breed new breeds, using mainly inbreeding;

M.F. was bred in this way. Ivanov developed the “Ukrainian White Steppe” pig breed, which combined the qualities of Ukrainian pigs and the white English breed. The new species had high levels of meat and tolerance to local environmental conditions.

Rice. 2. Interbreeding scheme.

“Heterosis effect” - manifests itself in the first generation during interbreeding, while quality indicators improve (broiler chickens);
Artificial insemination - used to obtain offspring from the best males;
Test on the resulting offspring - selection of males;
Embryo transplantation - with the help of this method it became possible to select embryos from the best cows and transfer them to other individuals;
Distant crossing is interspecific hybridization, which produces offspring with a set of qualities of two species. (For example, a mule is a cross between a horse and a donkey.)

Rice. 3. An example of distant hybridization.

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What have we learned?

The main methods of animal selection, like those of plants, are selection and crossing, but, unlike them, they are more complex and have a number of features. Breeders are developing new breeds that are more resistant to local natural conditions, have high quality indicators, are resistant to diseases, and help save on costs.

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This is the science of creating new and improving existing animal breeds, plant varieties, and strains of microorganisms. Selection is based on methods such as hybridization and selection. The theoretical basis of selection is genetics.

To successfully solve the problems facing selection, Academician N.I. Vavilov especially emphasized the importance of studying the varietal, species and generic diversity of crops; studying 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 characteristics: productivity, morphological, physiological characteristics.

Each breed of animal, 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.

To be successful, a breeder needs varietal diversity of the source material. At the All-Union Institute of Plant Growing 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 work on the selection of any crop.

The centers of origin of cultivated plants identified by N.I. Vavilov

Centers of origin	Location	Cultivated plants
1. South Asian tropical	Tropical India, Indochina, Southeast Asian Islands	Rice, sugar cane, citrus fruits, eggplants, etc. (50% cultivated plants)
2. East Asian	Central and Eastern China, Japan, Korea, Taiwan	Soybean, millet, buckwheat, fruit and vegetable crops - plum, cherry, etc. (20% of cultivated plants)
3. South-West Asian	Asia Minor, Central Asia, Iran, Afghanistan, South-West India	Wheat, rye, legumes, flax, hemp, turnips, garlic, grapes, etc. (14% of cultivated plants)
4. Mediterranean	Countries along the Mediterranean Sea	Cabbage, sugar beets, olives, clover (11% of cultivated plants)
5. Abyssinian	Abyssinian Highlands of Africa	Durum wheat, barley, bananas, coffee tree, sorghum
6. Central American	Southern Mexico	Corn, cocoa, pumpkin, tobacco, cotton
7. South American	West coast of South America	Potatoes, pineapple, cinchona

The richest in terms of the number of cultures are the ancient centers of civilization. It is there that the earliest farming culture took place, and artificial selection and plant selection have been carried out for a longer period of time.

The classical methods of plant breeding have been and remain hybridization and selection. There are two main forms of artificial selection: mass and individual.

Mass selection

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

Individual selection

Individual selection used in the selection of self-pollinating plants (wheat, barley, peas). In this case, the offspring retains the characteristics of the parental form, is homozygous and is called a pure line. Clean line- the offspring of one homozygous self-pollinated individual. Since mutation processes constantly occur, there are practically no absolutely homozygous individuals in nature. Mutations are most often recessive. They come under the control of natural and artificial selection only when they become homozygous.

Natural selection

This type of selection plays a decisive role in selection. Any plant is affected by a complex of environmental factors during its life, and it must be resistant to pests and diseases, and adapted to a certain temperature and water regime.

Inbreeding (inbreeding)

In the center is heterotic corn, on the left and right are the parental individuals.

This is called inbreeding. Inbreeding occurs when cross-pollinated plants self-pollinate. For inbreeding, plants are selected whose hybrids provide the maximum effect of heterosis. Such selected plants undergo forced self-pollination for a number of years. As a result of inbreeding, many recessive unfavorable genes become homozygous, which leads to a decrease in plant viability and to their “depression.” Then the resulting lines are crossed with each other, hybrid seeds are formed, giving a heterotic generation.

Heterosis(“hybrid vigor”) is a phenomenon in which hybrids are superior to their parent forms in a number of traits and properties. Heterosis is characteristic of first-generation hybrids; the first hybrid generation gives an increase in yield of up to 30%. In subsequent generations, its effect weakens and disappears. The heterosis effect is explained by two main hypotheses. The 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 a dominant state in a genotype, the greater the effect of heterosis.

R	♀AAbbCCdd	×	♂aaBBccDD
F 1	AaBbCcDd

The overdominance hypothesis explains the phenomenon of heterosis by the overdominance effect. 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 some genes become homozygous.

Diploid plants (2 n= 16) and tetraploid (2 n= 32) buckwheat.

Aa × Aa
AA 2Aa ahh

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

Method for obtaining polyploids. Polyploid plants have a greater mass of vegetative organs and larger fruits and seeds. Many crops are natural polyploids: wheat, potatoes; varieties of polyploid buckwheat and sugar beets have been bred.

Species in which the same genome is multiplied multiple times are called autopolyploids. The classic way to obtain polyploids is to treat seedlings with colchicine. This substance blocks the formation of spindle microtubules during mitosis, the set of chromosomes in cells doubles, and the cells become tetraploid.

Distant hybridization

Restoring the fertility of a cabbage-raspberry hybrid: 1 - cabbage; 2 - radish; 3, 4 - cabbage-raspberry hybrid.

Distant hybridization- This is the crossing of plants belonging to different species. Distant hybrids are usually sterile because meiosis is disrupted (two haploid sets of chromosomes from different species cannot conjugate) and, therefore, gametes are not formed.

A technique for overcoming infertility in distant hybrids was developed in 1924 by the Soviet scientist G.D. Karpechenko. He proceeded as follows. First I crossed the radish (2 n= 18) and cabbage (2 n= 18). The diploid set of the hybrid was equal to 18 chromosomes, of which 9 chromosomes were “rare” and 9 were “cabbage”. The resulting cabbage-radish hybrid was sterile, since during meiosis the “rare” and “cabbage” chromosomes were not conjugated.

Next, with the help of colchicine G.D. Karpechenko doubled the chromosome set of the hybrid, the polyploid began to have 36 chromosomes; during meiosis, “rare” (9 + 9) chromosomes were conjugated with “rare” chromosomes, “cabbage” (9 + 9) with “cabbage”. Fertility was restored. In this way, wheat-rye hybrids (triticale), wheat-wheatgrass hybrids, etc. were obtained. Species in which different genomes were combined in one organism, and then their multiple increase, are called allopolyploids.

Use of somatic mutations

Somatic mutations are used for the selection of vegetatively propagated plants. I.V. used this in his work. Michurin. By means of vegetative propagation it is possible to preserve a beneficial somatic mutation. In addition, only through vegetative propagation are the properties of many varieties of fruit and berry crops preserved.

Experimental mutagenesis

Based on the discovery of the effects of various radiations to produce mutations and the use of chemical mutagens. Mutagens make it possible to obtain a wide range of different mutations. Nowadays, more than a thousand varieties have been created in the world, descending from individual mutant plants obtained after exposure to mutagens.

Plant breeding methods proposed by I.V. Michurin

Using the mentor method I.V. Michurin sought to change the properties of the hybrid in the desired direction. For example, if it was necessary to improve the taste of a hybrid, cuttings from a parent organism with good taste were grafted into its crown, or a hybrid plant was grafted onto a rootstock, towards which it was necessary to change the qualities of the hybrid. I.V. Michurin pointed out the possibility of controlling the dominance of certain traits during the development of a hybrid. To achieve this, exposure to certain external factors is necessary in the early stages of development. For example, if hybrids are grown in open ground, their frost resistance increases on poor soils.

The term “selection” itself comes from the Latin word “selection”. This science studies ways and methods of creating new and improving existing groups (populations) of organisms used to support the life of humanity. We are talking about varieties of cultivated plants, breeds of domestic animals and strains of microorganisms. The main criterion is the value and stability of new features and properties in practical activities.

Breeding of plants and animals: main directions

High yields of plant varieties, fertility and productivity of animal breeds.
Quality characteristics of products. In the case of plants, this may include taste, appearance of fruits, berries and vegetables.
Physiological signs. In plants, breeders most often pay attention to the presence of precocity, drought resistance, winter hardiness, resistance to diseases, pests and adverse effects of climatic conditions.
Intensive path of development. For plants, this is a positive dynamics of growth and development when applying fertilizers, watering, and for animals, it is “payment” for food, etc.

Selection at the present stage

Modern selection of animals, plants and microorganisms, in order to increase efficiency, necessarily takes into account the needs of the market for agricultural products, which is especially important for the development of a specific industry of a particular production. For example, baking high-quality bread with good taste, elastic crumb and crispy crumbly crust should be made from strong (vitreous) varieties of soft wheat, which contain a large amount of protein and elastic gluten. Higher grades of cookies are made from mealy varieties of soft wheat, while durum wheat varieties are best suited for the production of pasta.

Oddly enough, the selection of animals and microorganisms are related. The fact is that the results of the latter are used in biological control of pathogens in animals, as well as various varieties of cultivated plants.

A striking example of selection based on taking into account market needs is fur farming. Growing fur-bearing animals, which differ in different genotypes responsible for the color and shade of the fur, depends on fashion trends.

Theoretical basis

In general, selection should develop on the basis of the laws of genetics. It is this science, which studies the mechanisms of heredity and variability, that makes it possible, through various influences, to influence the genotype, on which, in turn, the set of properties and characteristics of the organism depends.

Also, the methodology in selection uses the achievements of other sciences. These are systematics, cytology, embryology, physiology, biochemistry, molecular biology and biology of individual development. Thanks to the high rates of development of the above-mentioned areas of natural science, new prospects in breeding are opening up. Already today, research in the field of genetics is reaching a new level, where targeted modeling of the necessary traits and properties of animal breeds, plant varieties and strains of microorganisms is possible.

Genetics plays a decisive role in the process of solving breeding problems. It allows, using the laws of heredity and variability, to plan the selection process in such a way as to take into account the peculiarities of inheritance of specific traits.

Selection of source genetic material

Selection of animals, plants and microorganisms can only be effective if the starting material is carefully selected. That is, the correct choice of initial breeds, varieties, species is determined by the study of their origin and evolution in the context of those properties and characteristics that need to be endowed with the proposed hybrid. In the search for the required forms, the entire global gene pool is taken into account in strict sequence. Thus, the priority is to use local forms with the necessary characteristics and properties. Next, forms that grow in other geographical or climatic zones are attracted, that is, methods of introduction and acclimatization are used. The last resort is to resort to methods of experimental mutagenesis and genetic engineering.

Animal breeding: methods

In this area of science, the most effective methods are being developed and studied to breed new breeds of domestic animals and improve existing ones.

Animal selection has its own specifics, which is due to the fact that animals do not have the ability to reproduce vegetatively and asexually. They are characterized by only sexual reproduction. It also follows from this circumstance that in order to breed offspring, an individual must reach sexual maturity, and this affects the timing of research. Also, the possibilities of selection are limited by the fact that, as a rule, the offspring of individuals are few.

The main methods for breeding new breeds of animals, as well as plant varieties, can be called selection and hybridization.

Animal selection aimed at developing new breeds most often uses individual selection rather than mass selection. This is due to the fact that caring for them is more individualized compared to caring for plants. In particular, about 10 people look after a livestock of 100 animals. Whereas in the area where hundreds and thousands of plant organisms grow, from 5 to 8 breeders work.

Hybridization

One of the leading methods is hybridization. In this case, animal selection is carried out through inbreeding, unrelated crossing and distant hybridization.

Inbreeding refers to the hybridization of individuals that belong to different breeds of the same species. This method makes it possible to obtain organisms with new characteristics, which can then be used in the process of breeding new breeds or improving old ones.

The term "inbreeding" comes from the English words meaning "within" and "breeding." That is, crossing of individuals belonging to closely related forms of one population is carried out. In the case of animals, we are talking about insemination of closely related organisms (mother, sister, daughter, etc.). The expediency of inbreeding is based on the fact that the original form of a particular trait is decomposed into a number of pure lines. They usually have reduced viability. But if these pure lines are subsequently crossed with each other, heterosis will be observed. This is a phenomenon that is characterized by the appearance of an increase in certain characteristics in hybrid organisms of the first generation. These are, in particular, vitality, productivity and fertility.

Animal selection, the methods of which have fairly wide boundaries, also uses distant hybridization, which is a process directly opposite to inbreeding. In this case, individuals of different species are crossed. The goal of distant hybridization is to obtain animals that will develop valuable performance properties.

Examples include crossing a donkey and a horse, a yak and a tour. It should be noted that hybrids often do not produce offspring.

Research by M. F. Ivanov

The famous Russian scientist M. F. Ivanov was interested in biology from childhood.

Animal selection became the object of his research when he studied the features of the mechanisms of variability and heredity. Having become seriously interested in this topic, M.F. Ivanov subsequently developed a new breed of pig (white Ukrainian). It is characterized by high productivity and good adaptability to climatic conditions. For crossing, a local Ukrainian breed was used, well adapted to living conditions in the steppe, but having low productivity and low quality meat, and an English white breed, having high productivity, but not adapted to living in local conditions. Methodological techniques of inbreeding, unrelated crossing, individual mass selection, and education under conditions of detention were used. As a result of long-term painstaking work, a positive result was achieved.

Prospects for the development of breeding

At each stage of development, the list of goals and objectives of breeding as a science is determined by the specific requirements of agricultural and livestock technology, the stage of industrialization of crop and livestock production. For the Russian Federation, it is very important to create plant varieties and animal breeds that maintain their productivity in different climatic conditions.

Table 54. Basic selection methods (T.L. Bogdanova. Biology. Assignments and exercises. A manual for applicants to universities. M., 1991)

Methods	Animal breeding	Plant breeding
Selection of parent pairs	By economically valuable traits and by exterior (a set of phenotypic traits)	According to their place of origin (geographically distant) or genetically distant (unrelated)
Hybridization: a) unrelated (outbreeding)	Crossing distant breeds with contrasting characteristics to obtain heterozygous populations and the manifestation of heterosis. The result is infertile offspring	Intraspecific, interspecific, intergeneric crossing leading to heterosis to obtain heterozygous populations, as well as high productivity
b) closely related (inbreeding)	Crossing between close relatives to produce homozygous (pure) lines with desirable traits	Self-pollination in cross-pollinating plants by artificial influence to obtain homozygous (pure) lines
Selection: a) massive	Not applicable	Suitable for cross-pollinating plants
b) individual	Rigid individual selection is used for economically valuable traits, endurance, and exterior	It is used for self-pollinating plants, pure lines are isolated - the offspring of one self-pollinating individual
Method of testing sires by offspring	They use the method of artificial insemination from the best male sires, the qualities of which are checked by numerous offspring	Not applicable
Experimental production of polyploids	Not applicable	Used in genetics and breeding to obtain more productive, productive forms

In plant breeding, hybridization and selection are widely used - mass (without taking into account the genotype) and individual. In plant growing, mass selection is often used in relation to cross-pollinating plants. With this selection, only plants with desirable qualities are retained in the sowing. When re-sowing, plants with certain characteristics are again selected. Individual selection comes down to selecting individual individuals and obtaining offspring from them. Individual selection leads to the selection of a pure line - a group of genetically homogeneous (homozygous) organisms. Many valuable varieties of cultivated plants have been developed through selection. To introduce valuable genes into the gene pool of a created plant variety or animal breed and obtain optimal combinations of traits, hybridization is used followed by selection. When crossing different breeds of animals or plant varieties, as well as during interspecific crossings in the first generation of hybrids, viability increases and powerful development is observed. This phenomenon is called hybrid vigor, or heterosis. It is explained by the transition of many genes to a heterozygous state and the interaction of favorable dominant genes. With subsequent crossings of hybrids with each other, heterosis fades due to the separation of homozygotes.

Polyploidy is also used, thanks to which high-yielding polyploid varieties of sugar beet, cotton, buckwheat, etc. are bred. In this way, G. D. Karpechenko (1935) obtained an interspecific cabbage-radish hybrid. Each of the original forms had 9 chromosomes in the germ cells. In this case, the cells of the hybrid obtained from them had 18 chromosomes. But some eggs and pollen grains contained all 18 chromosomes (diploids), and when they were crossed, a plant with 36 chromosomes was created, which turned out to be fertile. Thus, the possibility of using a polyploid to overcome uncrossability and infertility during distant hybridization was proven.

One of the selection techniques is the breeding of pure lines through repeated forced self-pollination of plants: the offspring of such a plant becomes homozygous for all genes; Subsequently, individuals of two pure lines are crossed, which sharply increases the yield of first-generation hybrids and their viability. This phenomenon is called heterosis. However, in subsequent generations, heterosis decreases and yield decreases, and therefore only first-generation hybrids are used in practice.

Using the methods of crossing and individual selection by P. P. Lukyanenko, highly productive Kuban wheat varieties were developed: Bezostaya 1, Aurora, Caucasus; V.N. Remeslo in Ukraine received the Mironovskaya 808 variety, and then the more productive varieties Yubileinaya 50, Kharkovskaya 63, etc. V.S. Pustovoit and his employees using these methods created a sunflower variety in the Kuban containing up to 50–52% oil in the seeds .

Overcoming infertility of interspecific hybrids. For the first time this was accomplished in. in the early 20s to the Soviet geneticist G.D. Karpechenko when crossing radishes and cabbage. This newly created plant was neither radish nor cabbage. The pods occupied a sort of intermediate position and consisted of two halves, one of which resembled a cabbage pod, the other a radish.

Artificial mutagenesis. Natural mutations accompanied by the appearance of beneficial traits for humans occur very rarely. You have to spend a lot of time and effort searching for them. The frequency of mutations increases sharply when exposed to mutagens. These include certain chemicals as well as ultraviolet and x-ray radiation. These effects disrupt the structure of DNA molecules and cause a sharp increase in the frequency of mutations. Along with harmful mutations, beneficial ones are often discovered, which are used by scientists in breeding work. By exposure to mutagens in crop production, polyploid plants are obtained, which are distinguished by larger sizes, high yields and more active synthesis of organic substances. Radiation irradiation followed by selection created valuable varieties of peas, beans, and tomatoes.

A special place in the practice of improving fruit and berry crops is occupied by the selection work of I. V. Michurin. He attached great importance to the selection of parental pairs for crossing. At the same time, he did not use local wild varieties (since they had persistent heredity, and the hybrid usually deviated towards the wild parent), but took plants from other, distant geographical places and crossed them with each other. Using similar methods, such valuable varieties as the winter Bere Michurina pear were developed (from crossing the southern Bere Royal pear variety and the wild Ussuri pear) and the Bellefleur-Chinese apple tree (parents: the American variety Bellefleur yellow and the Chinese apple tree originally from Siberia).

An important link in Michurin’s work was the targeted education of hybrid seedlings: at a certain period of their development, conditions were created for the dominance of the traits of one of the parents and the suppression of the traits of the other, i.e., effective management of the dominance of traits (different methods of tillage, fertilization, grafting into the crown of the other plants, etc.). The mentor method was also used - education on a rootstock. As a scion, he took both a young plant and buds from a mature fruit-bearing tree. Using this method, it was possible to impart the desired color to the fruits of a cherry-cherry hybrid called “Beauty of the North.” Michurin also used distant hybridization. He obtained a unique hybrid of cherry and bird cherry - cerapadus, as well as a hybrid of thorn and plum, apple and pear, peach and apricot. All Michurin varieties are maintained through vegetative propagation.

Table. Methods of selection and genetic work by I. V. Michurina (T. L. Bogdanova. Biology. Assignments and exercises. A manual for applicants to universities. M., 1991)

Methods	Essence of the method	Examples
Biologically distant hybridization: a) interspecific	Crossing representatives of different species to obtain varieties with the desired properties	Vladimir cherry X Winkler white cherry = Beauty of the North cherry (good taste, winter hardiness)
b) intergeneric	Crossing representatives of different genera to obtain new plants	Cherry X bird cherry = Cerapadus
Geographically distant hybridization	Crossing representatives of contrasting natural zones and geographically distant regions in order to instill in the hybrid the necessary qualities (taste, stability)	Wild Ussuri pear X Bere royal (France) = Bere winter Michurina
Selection	Multiple, hard: in size, shape, winter hardiness, immune properties, quality, taste, color of fruits and their keeping quality	Many varieties of apple trees with good taste and high yield have been promoted to the north
Mentor method	Nurturing desirable qualities in a hybrid seedling (increasing dominance), for which the seedling is grafted onto a parent plant from which they want to obtain these qualities. The older, more powerful, and longer the mentor is, the stronger his influence.	Chinese apple tree (under howl) X hybrid (Chinese X Kandil-sinap) = Kandil-sinap (frost-resistant) Bellefleur-chinese (hybrid rootstock) X Chinese (scion) = Bellefleur-chinese (long-term late-ripening variety)
Mediator method	In distant hybridization, using a wild species as an intermediary to overcome uncrossability	Wild Mongolian Almond X Wild David's Peach = Almond Mediator Cultivated peach X almond Intermediary = hybrid peach (advanced north)
Exposure to environmental conditions	When raising young hybrids, attention was paid to the method of storing seeds, the nature and degree of nutrition, exposure to low temperatures, soil poor in nutrition, and frequent transplants	Hardening of a hybrid seedling. Selection of the hardiest plants
Pollen mixing	To overcome interspecific incompatibility (incompatibility)	The pollen of the mother's plant mixed with the pollen of the father's, its own pollen irritated the stigma, and it perceived foreign pollen

Animal selection differs from that of plants: animals produce few offspring, they reach sexual maturity later, they do not reproduce vegetatively, and they lack self-fertilization. However, hybridization and selection, both mass and individual, are also used in animal selection. They take into account the exterior characteristics of the parent pairs, the pedigree of the producers, and check the purity of the breed. Through inbreeding (inbreeding), pure lines are obtained when all or most genes become homozygous.

Creating a white steppe Ukrainian breed of pigs, academician. M.F. Ivanov took a highly productive English boar and a fertile Ukrainian pig (uterus), unpretentious to the conditions of detention, as the initial forms for crossing. Then he backcrossed the resulting hybrids with the same boar. This is how the boar Ascanius I of excellent physique (weight 479 kg) was bred, which he then crossed with his sisters, daughters, and granddaughters. In parallel to this inbred line, other similar lines were obtained. Despite the fact that within each inbred line individuals with reduced viability and other undesirable traits arose, most genes were transferred to a homozygous state. By further crossing two pure lines with each other, followed by repeated individual selection, a breed of steppe white Ukrainian pig was obtained, combining high productivity, fertility and stability.

First generation hybrids obtained from crossing individuals of two inbred lines are usually characterized by pronounced heterosis. This is widely used in animal husbandry to obtain economically valuable forms.

Crossing unrelated individuals is called outbreeding. It is carried out between individuals of different breeds of the same animal species and even within different genera and species, i.e., during distant hybridization. In this way, an infertile hybrid of a donkey and a horse was obtained - a mule, a hybrid of a one-humped and two-humped camel, a hybrid of a yak and cattle (their males are infertile, and the females are fertile). These hybrids are characterized by heterosis, i.e. increased vitality, have longevity and greater endurance compared to their parents.