Selection is the science of creating new and improving existing animal breeds, plant varieties and strains of microorganisms. The theoretical basis of selection is genetics.
Selection tasks :
Increasing the productivity of plants, animals and microorganisms
Breeding new breeds, varieties, strains
Ensuring maximum production with minimum costs
To solve these problems it is necessary:
Knowledge of the patterns of inheritance of traits
Study of hereditary variability
Study of modification variability (the influence of the environment on the development of traits)
Study of varietal, species and generic diversity of crops
Development of artificial selection strategies and methods
Breeds of animals, varieties of plants and strains of microorganisms are populations of organisms artificially created by man, with a characteristic set of traits fixed hereditarily (productivity). Strains - the offspring of one cell, a pure culture, but at the same time different strains can be obtained from one cell.
Often cultivated plants and domestic animals cannot live without humans, since as a result of selection, organisms have been instilled with traits that are beneficial to humans, but harmful to the organisms themselves.
In Russia, the founder of selection is considered Nikolay Vavilov .
Installed 8 centers of origin cultivated plants, because during expeditions he studied their diversity and wild ancestors in different places around the globe.
Formulated law of homological series heredity and variability: species and genera that are genetically close are characterized by similar series of genetic variability. Knowing what forms of variability are observed in one species, one can predict the discovery of similar forms in a related species. This is because related species evolved from a common ancestor through natural selection. That is, the descendants inherited approximately the same set of genes from him and the resulting mutations should be similar.
The law applies to plants and animals: albinism and lack of feathers in birds; albinism and hairlessness in mammals. In plants, parallelism is observed in the following characters: bare and filmy grains, awned and awnless ears.
For breeding and agriculture, this makes it possible to find in related species a characteristic feature that is absent in one, but present in others. Medicine receives material for its research, since it is possible to study human diseases using animals with homologous diseases. For example, diabetes mellitus in rats, congenital deafness in mice, cataracts in dogs, etc.
Hybridization
The process of obtaining hybrids is based on combining the genetic material of different cells and organisms. Hybrids can be obtained during the sexual process by combining somatic cells. Hybridization: interspecific and intraspecific (related and unrelated)
1) Inbreeding - inbreeding of organisms with common ancestors. Characteristic of self-pollinating plants and hermaphroditic animals.
Hard - crossing close relatives: mother and son, brother and sister
Soft - crossing of related organisms in 4 and subsequent generations
With each generation, the homozygosity of hybrids increases, and since many harmful mutations are in recessive genes; they manifest themselves in a homozygous state. The consequence of inbreeding is the weakening and degeneration of descendants. Inbreeding produces clean lines , rare desirable characteristics are fixed.
2) Outbreeding - unrelated crossing of organisms, without family ties over the previous 6 generations. This is the crossing of representatives of the same species, but different lines, varieties, breeds. They are used to combine the valuable properties of various lines, to increase the viability of breed or varietal lines, which helps prevent their degeneration.
Heterosis - a phenomenon in which the first generation of hybrids has increased productivity and viability compared to the parent forms.
Full manifestation of heterosis is observed only in the first generation, since most alleles become heterozygous. Then they gradually pass into a homozygous state and the effect of heterosis weakens. It is used in agriculture, as clean lines are always maintained in plant breeding. Heterosis of plants can be reproductive, somatic and adaptive.
4) Distant or interspecific hybridization - crossing two individuals of different species. Used to combine valuable qualities of individuals of different species. This is how hybrids were obtained: wheat and wheatgrass, rye and wheat = triticale, cherry and bird cherry = ceropadus, beluga and sterlet = bester, stallion and donkey = hinny, ferret and mink = honorik, hare hare and white hare = cuff.
Wild argali sheep and fine-wool merino sheep = arharomerinos
Mare and donkey = mule, hardy, strong, sterile, with a long lifespan and increased vitality.
Problem - infertility interspecific hybrids. This occurs due to the fact that different species have different numbers and structure of chromosomes, therefore the conjugation and process of chromosome segregation during meiosis is disrupted.
Overcoming infertility in animal hybrids is especially difficult. In 1924 Karpechenko created a cabbage-radish hybrid and for the first time overcame infertility using the method polyplodization . He crossed radish and cabbage (2 n -18; n -9 HR-m). But during meiosis, the chromosomes did not conjugate or separate; the hybrids were sterile. Then, using colchicine, which blocks the formation of spindle microtubules, Karpechenko doubled the chromosome set of hybrids to tetraploid (4 n -36, 2 n -18). As a result, conjugation, the formation of gametes and restoration of fertility became possible.
It has become possible to produce hybrids in animals using cell engineering.
Selection
Artificial selection - creation of new breeds and varieties through the systematic preservation and reproduction of individuals with certain characteristics. At first, selection was carried out unconsciously: man carried it out from the beginning of the domestication of animals. Modern selection is carried out consciously, based on knowledge of selection and genetics, that is, the laws of heredity and variability.
The theoretical foundations were put forward by Charles Darwin. He proved that varieties and breeds have one common ancestor and are not independent species. Man formed varieties and breeds according to his own interests, often to the detriment of the viability of animals.
- massive aimed at preserving the group. Used primarily for microorganisms and cross-pollinated plants. Selection is carried out according to phenotype , thereby the desired trait is increasingly developed.
- individual aimed at preserving individuals. It is used for self-pollinating plants (obtaining pure lines) and animals. Since the period for producing offspring in animals is quite long, selection is carried out according to genotype , individual individuals are left for reproduction.
Mutagenesis
Mutagenesis is the production of mutations using physical and chemical agents. For example method polyplodization , the effect of which is achieved by exposure to the poison colchicine, which destroys the filaments of the spindle.
Features of selection
1) Plants
Sexual and asexual reproduction is typical; mass selection based on phenotype is used. Various forms of hybridization. Polyploidy is used to increase the resistance of varieties and overcome the sterility of hybrids.
Michurin – mentor method : directed influence of the parent plant on the properties of the young hybrid after grafting.
Features of animal selection
Animals reproduce only sexually, which significantly limits selection methods. The main methods are individual selection and various forms of hybridization. In agriculture, the phenomenon of heterosis and artificial insemination are used.
Astaurov - silkworm by polyplodization.
Ivanov – Ukrainian white steppe pig by interspecific hybridization
Features of microorganism selection
The bacterial genome is haploid, represented by one circular DNA molecule, so any mutations appear already in the first generation. However, a very high reproduction rate facilitates the search for mutants. The main methods are experimental artificial mutagenesis and selection of the most productive strains. This is how a strain of the penicillium fungus was obtained, the productivity of which was increased several times.
Modern additional breeding methods .
1. Artificial insemination.
2. Hormonal super-ovulation.
3. Embryo transplantation.
Darwin's views
Darwin studied methods of breeding new breeds and established stages: the breeder selects individuals with the characteristics he needs; receives offspring from them; selects individuals in which the desired trait is better expressed. After several generations, the trait is fixed, becomes stable, and a new breed or variety is formed.
Thus, the selection is based on the following factors:
1. The initial diversity of an individual, that is, their natural variability.
2. Transmission of traits by inheritance.
3. Artificial selection.
Fill out an application to prepare for the Unified State Exam in biology or chemistry
Brief feedback form
Lesson in 9th grade “Genetic bases of selection of organisms. Tasks of modern selection"
Target: give an idea of selection, its methods, goals and results, show that the theoretical basis of selection is genetics.
Equipment and material: tables depicting animal breeds and plant varieties.
Basic concepts and terms: selection, artificial selection, breed, variety, strain, zoning, hybridization, unconscious selection, methodical selection, mass selection, individual selection.
Lesson structure and content
1. Updating basic knowledge and motivating learning activities
Questions for students.
1) What varieties of plants and animal breeds do you know?
2) How did breeders obtain these varieties and breeds?
3) how do breeders obtain such a variety of varieties?
4) Can knowledge about the genetic characteristics of organisms contribute to selection processes?
2. Learning new material
Teacher's story.
Tasks and methods of modern selection.
Breeding is the science of methods for creating varieties of plants, animal breeds and strains of microorganisms with traits desired by humans. She achieved the most significant successes with the active use of genetics, which was the theoretical basis of selection. In the selection process, as a rule, several stages are distinguished:
Justification of the purpose and objectives of selection;
Creation and selection of source material;
Development of a selection scheme, selection process (including various selection methods);
Variety testing.
The emergence of scientific selection is associated with the evolutionary teachings of Charles Darwin, the experimental studies of G. Mendel, V. Johansen, and breeders I. V. Michurin, L. Burbank, whose work served as the basis for the development of the theory of selection. In turn, discoveries in genetics contributed to the development of methods for the selection process and increased efficiency of artificial selection. For example, the discovery of Mendel’s laws made it possible to purposefully select pairs for crossing, and N.I. Vavilov’s establishment of the centers of origin of cultivated plants and the substantiation of the law of homological series of hereditary variability made it possible for breeders to develop methods for effectively searching for source material. The study of the nature of inheritance of economically valuable traits contributed to the creation of a whole system of crossings and made it possible to combine various plant properties.
N.I. Vavilov did a lot to develop the theoretical foundations of selection and clarify the definition of selection as an independent science. Giving a general definition of selection as a science, N. I. Vavilov wrote: “Selection is essentially human intervention in the formation of animals and plants; in other words, selection is an evolution directed by the will of man.” N. I. Vavilov emphasized the high degree of complexity of selection as a scientific discipline and believed that it consists of:
Teachings about source material;
Doctrines about hereditary variability;
Teachings about the role of the environment in identifying varietal characteristics;
Theories of hybridization;
Theories of the selection process;
The doctrine of the main directions in selection work (for example, selection is not immunity);
Private selection.
The use of various methods in the selection process led to the creation of a new direction - synthetic selection. It is based on the use of source material created by hybridization of various varieties and forms. The basis of synthetic selection is recombination and transgression. In combinational synthetic selection, one hybrid plant combines the characteristics and properties of two or more parental forms. The breeder’s task is to select and genetically stabilize hybrid plants that combine these traits and properties most successfully. Transgressive synthetic selection is based on selection in the generation of individuals with transgressions that split after hybridization, i.e., with positive traits that are more pronounced than those of the parents. The success of transgressive synthetic selection depends on the correct identification of parental pairs capable of producing transgressions when crossed.
Presentation of material about plant varieties, animal breeds, strains of microorganisms.
A story about the forms of artificial selection.
3. Generalization, systematization and control of students’ knowledge and skills
Conversation.
1) Name the areas of practical application of genetics.
2) List the main tasks of modern selection.
3) What role does the diversity of initial breeding material play for selection?
4) Define: what is a variety?
4. Independent work of students
Give answers to questions.
1) What is the mechanism of artificial selection?
2) What are called strains?
3) What is the name of a set of measures aimed at checking the compliance of the properties of certain breeds or varieties with the conditions of a certain natural zone?
5) Why can’t varieties and breeds be called species?
5. Homework
The theoretical basis of selection and seed production is genetics - the study of the laws of heredity and variability of organisms. Its position on the discreteness of heredity, the doctrine of mutations and modifications, the concepts of genotype and phenotype, dominance and recessiveness, homo- and heterozygosity, the establishment of the nature of heterosis, transgressions and neoplasms during hybridization, all achievements of genetics are of utmost importance for the development of effective methods of selection and seed production of agricultural crops crops
To develop effective methods for creating varieties and hybrids with high technological and nutritional qualities of grain, it is necessary to study the genetic and physiological-biochemical patterns of heredity and variability in carbohydrate content, fractional and amino acid composition of proteins in grain, the nature of variability and inheritance of grain quality traits in wheat, malting barley, millet, seeds of grain legumes and oilseeds and formulate the theoretical foundations of transgressive selection based on traits that determine the qualitative composition of the main substances (protein, oil, etc.). It is important to further improve the method of electrophoresis of storage proteins of wheat and barley grain for the selection of parental forms during hybridization and the selection of the most valuable recombinants for grain quality, frost resistance, disease resistance and other economically valuable traits, as well as for biotypic analysis of varieties in the primary stages of seed production. It is very important to study the genetic basis and morphological and anatomical features of the resistance of cereals to lodging and shedding and to create resistant varieties. It is necessary to develop and improve methods for obtaining new forms of plants using polyploidy, haploidy, culture of hybrid embryos, as well as cellular, chromosomal and genetic engineering.
Genetics substantiated the use of individual selection methods and developed the theory of crossings. One of the most important tasks of breeding is the creation of varieties that produce high quality products. Grain of new highly productive varieties and hybrids of grain crops must have excellent technological and nutritional qualities, stable under changing growing conditions. In our country, more than 60 varieties of strong wheat have been bred and zoned (Bezostaya 1, Mironovskaya 808, Donskaya Bezostaya, Odesskaya 51, Obriy, Saratovskaya 29, Saratovskaya 44, Tselinnaya 60, Novosibirskaya 87, etc.), which serve as an excellent source material for creating more more high-quality varieties for all climatic zones. Among the new zoned varieties of spring wheat, Saratovskaya 54 stands out in terms of technological qualities of grain. This variety is characterized by a consistently high protein content in the grain and a high volumetric yield of bread, as well as its better porosity. Its gluten quality is higher than that of the Saratovskaya 29 variety. Among the samples of the world collection there are varieties and forms that have exceptionally high grain quality - they contain from 18 to 22% protein (samples from China, Canada, India). They are successfully used in hybridization. New wheat varieties should have a higher protein content (15-16%) and high quality gluten.
It is necessary to create varieties of winter and spring wheat that combine high yield (7-9 and 5-6 tons per 1 ha, respectively) with a high protein content in the grain (16-17 and 18-19%), high-quality gluten and improved amino acid composition. The most important task of breeding is to develop varieties with consistently high yields and grain quality under different weather conditions. The creation of high-protein varieties and hybrids of corn, wheat, barley and oats with a high content of lysine and other essential amino acids is also a very important breeding problem.
The task is to develop new varieties and hybrids of sunflower with seed oil content of 58-60%. At the same time, it is important to improve the quality of the oil, i.e. a certain composition of fatty acids, lipid ratio, and increased vitamin content. The creation of a new mutant variety Pervenets, containing up to 75% oleic acid in oil versus 30-35% in conventional varieties, shows the enormous opportunities available in sunflower breeding for product quality.
Selection of grain legumes should be carried out for increased protein content. It is necessary to create varieties of sugar beets with increased sugar content and high technological qualities, new technical varieties of potatoes with a large amount of starch and protein in the tubers. The most important task in the breeding of fiber flax and cotton is the development of new high-yielding varieties that give high yield and quality of fiber.
To successfully solve the problem of plant immunity, it is of great importance to improve methods for creating infectious backgrounds and determining the racial composition of rust of grain crops, late blight of potatoes and other most dangerous diseases. It is necessary to develop methods for identifying genes and donors of resistance to diseases and pests, to study the conditions for the manifestation of their action and the nature of inheritance of this property depending on the selection of parental pairs and weather conditions. Computers and mathematical modeling should be used to organize information-genetic systems for registration and documentation of breeding material, develop models of varieties and breeding programs, objective selection of parental pairs, and select the optimal breeding strategy.
It is necessary to continue to develop issues of organization and economics of industrial seed production, to improve methods of accelerated propagation and the introduction of new varieties and hybrids into production; develop cultivation technologies in relation to the conditions of various soil and climatic zones; high-yielding seeds at all levels of the seed production system; improve methods and schemes of primary seed production; continue research to identify the best environmental and agrotechnical conditions for the formation of high-yielding seeds.
The variety plays a very important role in the development of energy- and resource-saving technologies for cultivating agricultural crops. This is achieved by sowing lodging-resistant varieties of grain crops and non-shattering varieties of peas, which allows harvesting by direct combining, early ripening hybrids of corn and sunflower with rapid drying of grain and seeds during ripening, which reduces the cost of electricity or fuel for drying, early deciduous varieties of cotton , which makes it possible to carry out machine harvesting of raw cotton with high productivity and without losses, etc.
Plant breeding is the most important factor in accelerating scientific and technological progress in agriculture. In recent years, it has been rapidly developing in our country and abroad. Important practical results have been obtained based on the development of highly effective methods for creating new varieties. These primarily include the breeding of short-stemmed varieties of wheat and rice, which make it possible to obtain a yield of more than 10 tons per 1 hectare on a high agricultural background, the creation of hybrid corn and hybrid sorghum with a potential yield of 15 tons per 1 hectare, the development of methods for radically improving the amino acid composition of the protein of the most important grains and grain feed crops, the creation of varieties of some crops that are resistant to dangerous diseases, doubling the oil content of sunflower seeds and other achievements. Selection and well-established seed production have become of paramount importance in increasing the yield and gross yield of grain and other agricultural crops.
Further development of this science led to the development of fundamentally new methods for creating source material and techniques for managing heredity. Along with classical methods of obtaining source material through hybridization, the use of local varieties and natural populations, new genetic methods are playing an increasingly important role: heterosis, experimental mutagenesis, polyploidy, haploidy, tissue culture, somatic hybridization, chromosomal and genetic engineering. The use of these methods in the breeding process has already yielded positive results.
The Main Directions of Economic and Social Development set the task of strengthening, through the use of biotechnology and genetic engineering, the creation and introduction into production of new highly productive varieties and hybrids of agricultural crops that meet the requirements of intensive technologies, are resistant to adverse environmental influences, are suitable for machine harvesting and satisfy requests from the food industry; improve the organization of seed production and improve the quality of seeds.
WHAT IS SELECTION.
The word "selection" comes from the Latin. "selectio", which translated means "choice, selection". Breeding is a science that develops new ways and methods for obtaining plant varieties and their hybrids, and animal breeds. This is also a branch of agriculture that deals with the development of new varieties and breeds with properties necessary for humans: high productivity, certain product qualities, resistance to diseases, well adapted to certain growth conditions.
GENETICS AS THE THEORETICAL BASIS OF SELECTION.
The theoretical basis of selection is genetics - the science of the laws of heredity and variability of organisms and methods of controlling them. She studies the patterns of inheritance of traits and properties of parental forms, develops methods and techniques for managing heredity. By applying them in practice when breeding new varieties of plants and animal breeds, a person obtains the necessary forms of organisms, and also controls their individual development and montogenesis. The foundations of modern genetics were laid by the Czech scientist G. Mendel, who in 1865 established the principle of discreteness, or discontinuity, in the inheritance of traits and properties of organisms. In experiments with peas, the researcher showed that the characteristics of parent plants during crossing are not destroyed or mixed, but are transmitted to the offspring either in a form characteristic of one of the parents, or in an intermediate form, again appearing in subsequent generations in certain quantitative ratios. His experiments also proved that there are material carriers of heredity, later called genes. They are special for each organism. At the beginning of the twentieth century, the American biologist T. H. Morgan substantiated the chromosomal theory of heredity, according to which hereditary characteristics are determined by chromosomes - the organelles of the nucleus of all cells of the body. The scientist proved that genes are located linearly among chromosomes and that genes on one chromosome are linked to each other. A trait is usually determined by a pair of chromosomes. When germ cells form, paired chromosomes separate. Their full set is restored in the fertilized cell. Thus, the new organism receives chromosomes from both parents, and with them inherits certain characteristics. In the twenties, mutation and population genetics arose and began to develop. Population genetics is a field of genetics that studies the main factors of evolution - heredity, variability and selection - in specific environmental conditions of a population. The founder of this direction was the Soviet scientist S.S. Chetverikov. We will consider mutation genetics in parallel with mutagenesis. In the 30s, geneticist N.K. Koltsov suggested that chromosomes are giant molecules, thereby anticipating the emergence of a new direction in science - molecular genetics. It was later proven that chromosomes consist of protein and deoxyribonucleic acid (DNA) molecules. DNA molecules contain hereditary information, a program for the synthesis of proteins, which are the basis of life on Earth. Modern genetics is developing comprehensively. It has many directions. The genetics of microorganisms, plants, animals and humans are distinguished. Genetics is closely related to other biological sciences - evolutionary science, molecular biology, biochemistry. It is the theoretical basis of selection. Based on genetic research, methods have been developed for producing hybrids of corn, sunflower, sugar beet, cucumber, as well as hybrids and crossbreeds of animals that have heterosis due to heterosis (heterosis is accelerated growth, increased size, increased viability and productivity of first generation hybrids compared to parental organisms )increased productivity.
