Basics of selection. Breeding methods
Selection is one of the most important areas of practical application of genetics, that is, genetics is the theoretical basis of selection, since genetics helps to rationally plan selection work based on from the laws of heredity and variability and specific features of inheritance of a certain trait.
In addition, selection is based on the achievements of other sciences, for example, plant systematics and geography, cytology, embryology, biochemistry and physiology of plants and animals, molecular biology, etc.
Breeding is the science of methods for creating new and improving existing breeds of domestic animals and varieties of cultivated plants and strains of microorganisms.
Selectionis an evolutionary process in which man is the main active factor and directs the entire process in accordance with his needs.
Breed, variety, strainis a population of organisms artificially created by man, which is characterized by certain hereditary characteristics. All individuals within a variety, breed or strain have a similar genotype, phenotype and the same type of reaction to the influence of environmental factors, for example, dairy breeds of cattle differ in milk yield, percentage of fat content and protein content in milk.
Variety valuedetermined by yield, nutritional and feed properties.
Breed value determined by the quality and quantity of the products received.
Main tasks of selection:
- increase in productivity varieties of cultivated plants, increasing the productivity of breeds of domestic animals and strains of microorganisms;
- quality improvement products (flax properties, gluten content in grain, amount of sugar in beets, etc.);
- improvement of physiological properties (earliness, frost resistance, etc.);
- promotion intensity of development (for plants - for feeding, for animals - for living conditions).
Conditions for successfulselection work:
Source material (variety, breed or species);
Studying the role of mutations in the appearance of a certain trait;
Study of patterns of inheritance during hybridization;
The role of the environment in the development of a trait;
Application of artificial selection.
(A striking example of selection taking into account the needs of the market is fur farming, since the cultivation of mink and sable foxes follows changing fashions. Of particular importance is the selection of insects for biological control methods. Soft varieties of wheat are needed to make cookies, and hard varieties are needed to make pasta. Breeds of chickens have been developed that do not reduce productivity in conditions of high crowding in poultry farms. For Belarus, it is important to create plant varieties that are productive in conditions of snowless, frosty winters and in conditions of late frosts.)
The success of breeding work is verystrongly depends on the genetic diversity of the original group of organisms.The gene pool of existing breeds and varieties is much smaller than the gene pool of wild species.
In order to study the diversity and geographical distribution of cultivated plants, N. I. Vavilov conducted a number of expeditions around the globe, collected huge seed material and isolatedcenters of origin of cultivated plants:
1) South Asian ( India ) - the birthplace of rice, bananas, citrus fruits, sugar cane;
2) East Asian(China) - the birthplace of soybeans, dew, buckwheat, apple, pear;
3) southwest asian(Central Asia) - the birthplace of wheat, peas, grapes;
4) Mediterranean- homeland of cabbage, beets, olives;
5) Abyssinian(Africa) - the birthplace of durum wheat, barley, coffee tree;
6) Central American(Mexico) - the birthplace of corn, cocoa, peppers, beans, cotton;
7) South American(South America) - the birthplace of potatoes, tobacco, sunflowers.
Vavilov’s research allows breeders to quickly select source material and, to a certain extent, predict the results.
Raw material:
Wild forms (they are distinguished by a number of useful properties, for example, resistance to sharp fluctuations in climatic factors, to diseases, have high fertility, but are inferior to cultivated ones in productivity);
Artificially obtained mutant forms;
Forms obtained as a result of combinative variability;
Varieties and breeds obtained in other climatic conditions.
Basic selection methods:
- - hybridization;
- obtaining clean lines;
- use of the phenomenon of heterosis;
- induced mutagenesis;
- use of polyploid forms;
- artificial selection.
G hybridization
A) inbreeding - closely related crossing;
b) outbreeding - unrelated crossing that is, crossing individuals of the same or different breeds or of the same or different varieties.
Artificial selection is the process by which better-adapted individuals are retained to reproduce.
In the early stages of human evolution, selection was unconscious, it started with domestication, that is, at first it was probably carried out selection by behavior(those individuals that were able to contact humans survived), and later, other signs began to be affected, the best individuals were left for the tribe.
At the present stage, they are used in breeding methodical selection:
A) mass- is carried out according to external phenotypic characteristics in the direction chosen by the breeder, its disadvantage is that it does not produce genetically homogeneous material, repeated selection is always necessary;
b) individual- based on genotype assessment.
With artificial selection, the hybrid is simultaneously affected by natural selection, which increases its adaptability to specific environmental conditions.
Currently, they are increasingly used in breedinginduced mutagenesis, which consists of an increase in the number of mutations as a result of exposure to various mutagens on the body.
A significant place in plant breeding is mainly given to obtainingpolyploid forms, since they are characterized by greater yield, colchicine is usually used, which destroys the spindle threads and prevents the divergence of homologous chromosomes during meiosis.
Breeding process coming on the way: source material → selection → hybridization → selection → hybridization → selection, etc.
Plant breeding:
1) setting a specific task;
2) selection of source material, (if it is not possible to find the necessary parental forms, artificial mutagenesis is used, and among the mutations that appear, useful ones are found, which are used in further work);
3) hybridization- is the production of hybrids from the crossing of genetically diverse organisms.
a) it is based on artificial pollination of usually cross-pollinated plants with its own pollen, such pollination leads to an increase in homozygosity and the consolidation of hereditary properties, and the offspring obtained from one homozygous plant by self-pollination is clean line.
Clean line is different decreased viability and decreased yield.
If then cross two clean lines between themselves - interline hybridization, then we get the phenomenon heterosis
Heterosis explained transition of most genes V heterozygous state. The phenomenon of heterosis can be fixed through vegetative propagation;
b) outbreeding- crossing unrelated organisms, however, such hybridization is carried out with difficulties, and interspecific and intergeneric hybrids are sterile, since conjugation of chromosomes of different species or genera is impossible during meiosis. For the first time, Karpechenko managed to overcome the sterility of interspecific hybrids, who obtained a hybrid of cabbage and radish (9 “rare” and 9 “cabbage” chromosomes) that was sterile, then the scientist obtained a polyploid form of the hybrid, which had 18 “rare” and “cabbage” chromosomes each, became conjugation of homologous chromosomes of cabbage with “cabbage” and radishes with “cabbage” is possible, with each gamete carrying 18 chromosomes (9 “rare” and 9 “cabbage”), such a hybrid became fertile. Thus, polyploidy has become one of the ways to restore fertility in interspecific plant hybrids.
Distant hybridization allows combine valuable characteristics of different species and even genera in one organism.
Difficulties in carrying out remote hybridization:
Mismatch of breeding cycles;
Incompatibility of pollen tubes.
Coping methods:
Method of vegetative rapprochement (preliminary grafting of one species onto another) (hybrid of rowan and pear);
Pollination with a mixture of pollen (apple + pear);
Intermediary method (hybrid of a wild species with a wild one, then with a cultivated one to increase frost resistance).
4) artificial selection consists of preserving for propagation plants with the desired characteristics:
A) mass selection
b) individual selection
With artificial selection, a variety is simultaneously affected by natural selection, which increases the adaptability of plants to specific environmental conditions.
The created variety is the result of human activity and the environment.
The development of new high-yielding plant varieties makes it possible to dramatically intensify agricultural production.
Successes in breeding work:
Academician P. P. Lukyanenko - winter wheat Bezostaya 1 - yield up to 100 c/ha, Aurora;
Shekhurdin and Mamontova - Saratovskaya29, Saratovskaya -36;
Academician N.V. Tsitsyn - a hybrid of wheat and rye - triticale - high milling qualities are combined with the ability to grow on poor soils;
Academician V. S. Pustovoit - a sunflower variety with an oil content in the seeds of over 20%;
A. N. Lutkov - new varieties of sugar beet with increased sugar content and productivity;
M.I. Khadzhinov - high-yielding varieties of corn;
P.I. Aismik - high-yielding potato varieties - Temp, Ogonyok, Lasunak, Sintez, etc.;
A. L. Semenov - perennial herbs;
A. G. Voluznev - varieties of black currant: Belarusian sweet, Katyusha, Partizanka, red currant: Beloved, gooseberry: Shchedry
Great contribution to plant breeding contributed by I.V. Michurin(1855-1935), devoted 60 years to breeding new varieties, worked in the city of Kozlov (now Michurinsk), Tambov region. At the beginning of his activities, he tried to acclimatize southern varieties by hardening in the northern regions, but they froze out, then he used selection methods. His work is based on a combination of three main methods:
- hybridization;
- selection;
- the impact of environmental conditions on developing hybrids (their “education” in the desired direction.
Michurin paid great attention to selection of initial parental forms for hybridization. He crossed local frost-resistant varieties with southern ones, and subjected the resulting seedlings to strict selection and contained in relatively severe conditions. This method was used to obtain the Slavyanka variety, a hybrid of Antonovka and southern Ranet pineapple.
Michurin attached particular importance crossing of geographically distant forms, not growing in the area where hybridization takes place. This method was used to develop the Bellefleur-Chinese variety, a hybrid of a Chinese apple tree from Siberia and the American variety Bellefleur yellow.
Michurin widely used distant hybridization:
He produced hybrids of raspberries and blackberries;
Rowan and hawthorn.
Michurin used for overcoming in carrying out distant hybridization the following techniques:
- vegetative rapprochement method(preliminary grafting of one species onto another leads to a change in the chemical composition of tissues, including generative organs, which increases the likelihood of pollen tubes sprouting in the pistil) (hybrid of rowan and pear);
- pollination with pollen mixture to stimulate the germination of pollen tubes, that is, “own” pollen irritates the stigma of the pistil and it perceives “foreign” pollen (apple + pear);
- mediator method(a hybrid of a wild species with a wild one, then with a cultivated one to increase frost resistance).
Most of the varieties bred by Michurin are complex heterozygotes, so to save them they use only vegetative propagation(layering, vaccinations).
Animal breeding:
The basic approaches do not differ from those in plant breeding, but there are peculiarities:
a) animals reproduce only sexually;
b) puberty occurs quite late;
c) a small number of descendants.
1) setting a specific task;
2) selection of parent pairs, When breeding animals, it is important to take into account exterior- this is a set of external characteristics of animals, their physique and the relationship of body parts. Different breeds of animals unequally react to changes in external conditions, for example, in meat breeds, improved nutrition leads to an increase in body weight, and in dairy breeds - to an increase in milk yield;
3) hybridization- is the production of hybrids from the crossing of genetically diverse organisms.
A) inbreeding - closely related crossing, it is based on the crossing of individuals of one generation or parents and offspring, which leads to increased homozygosity and consolidation of hereditary properties. Long-term inbreeding leads to weakening and even death, since many recessive mutations are detected in the homozygous state; to overcome these problems, after several inbreedings, outbreeding is used to increase heterozygosity;
If then cross two clean lines between ourselves - then we will get the phenomenon heterosis or hybrid power - this is increased viability and fertility in first generation hybrids, which decreases in subsequent generations.
There are 3 types of heterosis:
- reproductive- greater fertility than that of parents;
- somatic- increase in vegetative mass;
- adaptive- hybrids turn out to be better adapted.
Heterosis explained transition of most genes V heterozygous state, since in the heterozygous state mutant alleles do not appear.
The phenomenon of heterosis can be fixed by alternately crossing a hybrid with one or another original form.
b) outbreeding- crossing individuals of different breeds;
4) artificial selection consists of preserving for reproduction animals with the desired characteristics:
A) mass selection- selecting a group of organisms with the desired characteristics and obtaining offspring, and the selection is repeated from generation to generation, since individuals can split;
b) individual selection- growing the descendants of one individual, selection occurs faster, but the number of descendants is smaller.
With artificial selection, the breed is simultaneously affected by natural selection, which increases the adaptability of animals to specific environmental conditions;
5) method for determining the quality of sires by offspring(quantity and fat content of milk, egg production).
The created breed is the result of human activity and the environment.
Breeding new highly productive breeds of domestic animals can dramatically increase the quantity and quality of food products.
Successes in breeding work:
M. F. Ivanov - white steppe Ukrainian pig;
Breeds of fine wool sheep;
Sterile hybrids of horse and donkey - mules;
M. P. Grin - selection of black-and-white cattle;
V. T. Gorin - selection of pigs;
- interspecific hybrids- a mule (a hybrid of a mare and a donkey - sterile, but hardy, strong, long-lived), a hybrid between beluga and sterlet, a hybrid of carp and crucian carp, a hybrid of bull and yak.
Biotechnology is the human use of living organisms and biological processes for the industrial production of various products.
Biotechnology uses microorganisms (prokaryotes - bacteria and blue-green algae) and eukaryotes - fungi, microscopic algae.
The use of microorganisms in processes such as winemaking, bread baking, cheese making, etc., has been known since ancient times, but modern biotechnology arose in the mid-70s of the 20th century.
Features of microorganism selection are that scientists are practically not limited by either time or space, since microorganisms:
b) have simple regulation gene activity;
c) very fast reproduce;
d) have haploid set, therefore any mutation appears already in the first generation;
e) in a small number of test tubes and Petri dishes, millions of individuals can be grown in a few days, that is, easy to get several generations of organisms in almost a short time.
They are used in the selection of microorganisms natural abilities to synthesize substances useful to humans.
Stages of selection:
Isolation from wild nature of microorganisms capable of synthesizing the necessary compounds;
Selection of the most productive strains;
Induced mutagenesis and use selective media(media on which mutants grow well, but the original wild-type parents die);
Selection by productivity.
As nutrient medium For microorganisms, non-food products are used: liquid fractions of oil, synthetic alcohols, waste from the wood processing industry, etc.
Currently, biotechnology has gained great importance methods of cell and genetic engineering, which open up broad opportunities for genome rearrangement to obtain organisms with desired properties:
Thus, the gene responsible for the formation of insulin was included in the genome of Escherichia coli;
Strains of bacteria capable of destroying petroleum products have been constructed and are used to clean water during oil spills;
Strains of bacteria were constructed that produce large quantities of amino acids, vitamins, interferon, etc.
Method genetic engineering- This construction of new genetic structures according to a predetermined plan
Genetic engineering method includes:
- allocation from cells of individual genes or synthesis of genes outside cells;
- synthesis or gene cloning or transfer and integration of these genes into the genome using vectors;
- selection of cells with a recombinant genome.
This method became possible as a result of the discovery of enzymes restriction enzyme, which cut the DNA molecule in the right place and enzymes ligase which stitch together pieces of different DNA molecules and open vectors.
Vector is a short circular DNA molecule that can independently reproduce in a bacterial cell (virus, bacteriophage, specially constructed plasmid). First, the required gene is inserted into such a vector and then into the genome of the host cell.
Transgenic plants and animals- organisms whose genome has been changed through genetic engineering operations.
Cell engineering allows you to construct whole cells, as well as their individual fragments based on their cultivation, hybridization and reconstruction
- body cells are transferred into culture, and these cells synthesize substances necessary for humans, for example, ginseng cells transferred into culture synthesize medicinal raw materials, and induced mutagenesis or distant hybridization can be carried out with such cells to increase their productivity, for example, hybridomas of cells that synthesize antibodies with cancer cells that are capable of to endless synthesis;
- from regenerated plants are obtained from cultured and hybridized cells, for example, hybrids of tomato and potato, apple and cherry.
(However, manipulations at the genome level can lead to the emergence of strains with unpredictable properties, so progressive scientists held a conference calling for a moratorium on genetic engineering work; scientists began to work on obtaining mutant strains that cannot live in the natural environment and such organisms were obtained, they can live only on a nutrient medium and are not dangerous for living organisms).
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.
Features of plant breeding
From the very beginning of conscious activity, man sought to select for his use those plants that met human needs. This concerned various qualities of plants. For some purposes, certain taste qualities were required, for others, a certain appearance of the plant, for others, resistance to adverse environmental factors. In order to obtain plants with the desired qualities, such a branch of scientific and practical activity as breeding arose.
Definition 1
Selection is a set of methods of human activity aimed at creating new and improving existing varieties of living organisms (plant varieties, animal breeds and strains of microorganisms).
The peculiarity of plant selection is that vegetation and fruit ripening occur throughout the year. One plant can produce a large number of seeds. This means that when organizing experimental work, you can obtain large quantities of results within a year, which can be easily selected by phenotype and processed statistically.
General characteristics of plant breeding methods
As is known, the main methods of selection are hybridization and artificial selection. These methods are used simultaneously and complement each other.
Hybridization makes it possible to obtain organisms with a certain genotype, and artificial selection allows you to select organisms with certain external characteristics (phenotype) and continue work on their consolidation.
In addition, it is used in plant breeding grafting method . This makes it possible to artificially combine parts of different plants for further breeding work.
The effectiveness of breeding work depends on the diversity of the source material. Plant breeding can solve this problem. Using various forms of hybridization in combination with artificial mutagenesis. Thanks to the use of the latter and further selection among mutant forms, hundreds of new varieties of wheat, rye, barley and other cultivated plants were created. Now let's get acquainted with plant breeding methods in more detail.
Hybridization
Various forms of hybridization are used in plant breeding: intraspecific (closely related and unrelated) and interspecific crossing.
- This is considered to be closely related crossing , when the individuals being crossed have common close ancestors. This method allows you to obtain pure lines of plants with a high percentage of homozygosity for most traits.
- Unrelated crossing is carried out between plants of the same species, but without common ancestors. It allows you to combine different qualities of the same species in hybrids.
- Interspecific crossing is carried out between plants belonging to different species.
But quite often interspecific hybrids are sterile. The reason lies in the number of chromosomes in the karyotype of organisms. But modern science has learned to overcome the sterility of interspecific hybrids. For example, I.V. Michurin used the mediator method. To overcome the uncrossability of two plant species, he took a third plant, crossed it with the first, and crossed the resulting hybrid with the second plant.
Polyploidy
Definition 2
Polyploidy is the phenomenon of increasing the number of chromosomes in the nucleus of plant cells.
This is achieved in various ways. If chromosome doubling is not accompanied by cell division, then we can obtain a diploid germ cell, and then a triploid hybrid. There are also ways to obtain the phenomenon of polyploidy - the fusion of somatic cells or their nuclei; the formation of gametes with an unreduced number of chromosomes due to disruption of meiosis.
Geneticist G.D. Karpechenko used the method of influencing the spindle with various mutagens (chemicals, ionizing radiation, critical temperatures) in order to obtain gametes with a diploid set of chromosomes and obtain a tetraploid hybrid.
Mutations that lead to a multiple reduction in the number of chromosomes are also used. This makes it possible to quickly obtain plant forms that are homozygous for most genes.
Vaccination method
One of the classical methods of plant breeding is to artificially combine parts of different plants. A part (bud, shoot) of another plant is grafted onto a growing plant (rootstock). The part of the plant being grafted is called the scion. Grafting is not true hybridization. It only leads to non-heritable changes in the phenotype of the combined plant, without changing the genotype of the original forms. But grafting contributes to the convergence of the biochemical and physiological processes of the united plants. The purpose of this method is to enhance the desired changes in phenotype as a result of the combination of scion and rootstock properties (for example, the frost resistance of a northern rootstock and the palatability of southern scion varieties or the disease resistance of a rootstock). In addition, as a result of grafting, new qualities may appear that can be used in further breeding work.
Some varieties of cultivated plants, when propagated by seeds, quickly return to the phenotypes of their ancestral forms—they “go wild.” Therefore, the only way to maintain such varieties is either vegetative propagation or their grafting to wild animals.
Man continuously selects domestic animals, leaving the best ones that best meet his requirements (economic, aesthetic, etc.), using less valuable ones for consumer purposes. This is how animal selection appeared, which was initially unconscious, and then gradually began to take on the character of primitive methodical selection.
Origin of Pets
All domestic animals are descended from wild ancestors. Before other animals, the dog was domesticated in the middle of the Stone Age; its ancestors are the wolf and, possibly, the jackal.
At the end of the Stone Age, pigs, sheep, goats, cattle, and later horses were domesticated. Pigs come from wild European and Asian wild boars, sheep - from wild European sheep, goats - from ibex, cattle - from aurochs, horses - from tarpan and Przewalski's horse.
Features of selection
Thanks to selection over thousands of years, numerous local breeds have been formed, adapted to the specific conditions of various human habitats and their needs. Currently, when breeding new and improving existing breeds of domestic animals, breeders use, in principle, the same methods as in crop production.
But animal selection has a number of features:
- They reproduce sexually, therefore each breed is a complex heterozygous system;
- evaluate the qualities of males that cannot be verified externally (egg production, fat milk production), based on offspring and parents;
- in some species, puberty occurs quite late;
- few offspring are born.
The selection of producers based on economically valuable traits and animal appearance is of great importance. Exterior is a set of phenotypic characteristics of animals. The physique and size ratio of body parts are taken into account. Taking into account the exterior is important because the body represents a single whole. The functions of the body and its productivity are closely related to the structure of the body.
When breeding horses, pigs, sheep, and beef cattle, producers are evaluated by phenotype (exterior) and the quality of their offspring.
When breeding dairy cattle, selection is carried out in three stages. Preliminary selection of bulls is based on information about the milk production of mothers, grandmothers, sisters and exterior characteristics. The bulls are then assessed based on the productivity of their offspring.
Finally, sires identified as superior are crossed with daughters to see if they carry lethal or other undesirable genes. To obtain more offspring from the most valuable sires, artificial insemination is used.
Modern achievements
Animal breeding uses a wide range of methods for breeding valuable breeds. Old methods, proven by tests, and new ones, developed in the 20th century, are used. Cellular engineering is considered the latest and most promising. It is based on the transmission of hereditary information through somatic cells. Livestock specialists grow clones that could become an exact copy of the ancestor, with a set of appropriate qualities. In 1997, scientists managed to raise Dolly the sheep and several other animals using cloning.
Tsigai sheep Animal selection has helped produce a number of valuable breeds, examples of which are:
- Tsigai sheep - has high fertility and produces approximately 100 liters of milk in four months;
- black-and-white type of cattle - produces up to 5 tons of milk per year (fat content - 3.6-3.8%);
- Ascanian sheep - characterized by rapid growth (it reaches the size of an adult in a year and a half). The wool harvest reaches 20-30 kg from one ram.
Types of variability in animal breeding
Variation is the differences that arise between representatives of the same or different species, ancestors and offspring, under the influence of the genotype and the environment.
There are two types of variability:
- hereditary - manifests itself as a change in the genetic information of descendants.
- non-hereditary - manifested by a change in phenotype under the influence of external factors.
Hereditary variability is divided into mutational and combinative.
Mutational variability- occurs when genetic material is exposed to mutagenic factors. They arise spontaneously or as a result of the influence of temperature, radiation, and chemicals.
Combinative variability- characterized by a special combination of genes that are passed from parents to offspring. To obtain a new breed, several breeds are initially taken, after crossing which, in a planned order, species with the desired set of genes are obtained.
Methods
Breeders use the following methods to obtain new species: intrabreeding (inbreeding), interbreeding (outbreeding), heterosis, testing sires by offspring and artificial insemination.
Inbreeding(inbreeding) - in animal breeding they are used to preserve and improve the qualities of the breed. In practice, the best-performing species are selected and breeds that do not meet the requirements are culled.
For inbreeding, pairs for crossing with close family ties are selected: brothers and sisters, parents and their offspring. This is how homozygous species with valuable qualities are obtained. The disadvantage of the method is the weakening of animals, deterioration of adaptive capabilities and resistance to diseases.
Outbringing - unrelated crossing of animals belonging to different breeds and species. This method of crossing leads to heterosis. The goal of the method is to create new breeds that are amenable to further strict selection.
With the help of outbringing, a German Shepherd was obtained, which is used in all types of services, is well built, and is easy to train.
Heterosis - observed when crossing representatives of different breeds in the first generation. The resulting animals have a number of advantages compared to the parent forms. They grow faster and produce more milk or meat. For example, after crossing 2 meat types of chickens, broiler chickens are obtained that can effectively gain weight.
Testing of sires by offspring - They select males that do not exhibit certain qualities and cross them with daughters. This is how the quality of the resulting offspring is assessed in comparison with the maternal ones.
Artificial insemination - The method is used to fertilize females with the semen of the most productive males. Germ cells remain viable at low temperatures for a long time.
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 couples | 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.