Selection: basic terms and concepts. Basic methods of selection of plants, animals and microorganisms (hybridization, selection, polyploidy, artificial mutagenesis) Natural or artificial crossing of individuals belonging to
List the methods of selection work.
The main methods of selection include selection, hybridization, polyploidy, and artificial mutagenesis.
Artificial selection is the selection by man of the most economically valuable individuals of animals and plants in order to obtain from them offspring with desirable characteristics. Artificial selection is the most important method of selection and the main factor that determines the diversity of breeds of domestic animals and varieties of cultivated plants.
Hybridization is the natural or artificial crossing of individuals that differ in their characteristics and belong to different varieties, breeds, strains, and species. As a result of hybridization, hybrids are obtained.
Hybrids are formed by combining the hereditary material of genotypically different organisms and are characterized by new characteristics or new combinations of them.
Breeding also involves crossing organisms belonging to different types or even childbirth. In these cases, distant hybridization takes place - a rather complex process, since organisms belonging to different species, and even more so to different genera, have different genetic material (the number and structure of chromosomes). Very often, such crossing leads to the formation of infertile (sterile) hybrids that do not produce offspring. However, thanks to the painstaking work of breeding scientists, intergeneric hybrids have been obtained that are capable of reproducing.
Artificial mutagenesis is a selection method based on the exposure of organisms to mutagens that cause various mutations. New varieties and strains are often created based on these mutations. Ultraviolet and X-ray irradiation, exposure to neutrons or chemicals are usually used as mutagens. Artificial mutagenesis is especially widely used in the development of new strains of microorganisms.
Polyploidy is the production of polyploids, i.e. organisms in which the number of chromosomes is increased two, three or more times. This process is carried out by influencing the dividing cell by various factors that interrupt the divergence of chromosomes to the poles. As a result of the action chemical substances, ionizing radiation, high or low temperature, cell division is disrupted, and it becomes, for example, tetraploid (4n). Polyploids have higher yields, are richer in nutrients and are more resistant to unfavorable environmental factors.
Differences between mass selection and individual selection
How does mass selection differ from individual selection?
Mass selection is characterized by the fact that it is carried out only by phenotype, i.e., taking into account only the totality of the characteristics of the organism. Individuals with the desired characteristics are taken from the offspring and again crossed with each other. Mass selection is usually used for cross-pollinated plants and animals. This selection is aimed at maintaining a given breed or a certain variety at a given economic level.
In individual selection, a single individual is selected and through subsequent self-pollination in plants or closely related crosses in animals, pure lines are bred. Pure lines - groups of genetically homogeneous (homozygous) organisms - are valuable breeding material.
Heterosis
What is heterosis?
Heterosis manifests itself in the increased power of first-generation hybrids compared to parental forms. When crossing parental forms belonging to different breeds or varieties (to different pure lines), in first-generation hybrids a phenomenon called heterosis is observed.
Heterosis manifests itself in the fact that hybrids have outstanding qualities (greater height, weight, resistance to diseases, etc.) compared to the parent forms. The main reason for heterosis is that in heterozygotes, which are first-generation hybrids, harmful recessive gene alleles are not detected in the phenotype.
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What is a species?
A species is a collection of organisms characterized by a common origin, possessing hereditary similarity of all characteristics and properties, and capable of endlessly reproducing themselves through crossing.
Type criteria
What species criteria do you know?
Species criteria are the characteristic features and properties by which some species differ from others. There is no absolute criterion for a species. Various criteria only together make it possible to distinguish one species from another.
Morphological criterion - similarity of external and internal structure organisms.
The physiological criterion is the similarity of all life processes, and above all the similarity of reproduction, which determines the possibility of obtaining offspring through crossing.
Genetic criterion - a set of chromosomes characteristic of each species, their size, shape, DNA composition.
Ecological criterion - the place of a species in natural communities of organisms, its specialization, sets of factors external environment, necessary for the existence of the species.
Geographic criterion - the area of distribution of a species in nature (area).
The historical criterion is the community of ancestors, a single history of the emergence and development of the species.
Number of species on Earth
How many species live on our planet?
Scientists estimate that the Earth is inhabited by approximately three times as many species as have been recorded to date, with the figure likely being 4–5 million.
Population
What is a population?
A population is a group of organisms of the same species that have the ability to interbreed freely and maintain their existence in a given area indefinitely.
Conditions for the existence of the species
Why do species exist in the form of populations?
The existence of biological species requires appropriate conditions and resources necessary to support life. Conditions suitable for a particular species are formed in space as if in the form of separate “islands”. Species inhabit these “islands” that suit them and therefore are not distributed evenly throughout the territory, but in separate groups - populations.
Population properties
What properties can characterize a population as a group of organisms?
A population as a group of organisms is characterized by properties that cannot be applied to individual organisms. These properties are also called demographic indicators. Among them are: abundance (the total number of organisms), birth rate (the rate of population growth), mortality (the rate of population decline as a result of the death of individuals), age composition (the ratio of the number of individuals of different ages).
The Importance of Studying Populations
What is the practical significance of studying populations? Give examples.
The study of populations is important for predicting changes occurring in them and regulating them. For example, when harvesting wood, it is very important to know the rate of forest restoration in order to correctly plan the intensity of felling. The situation is similar with animal populations that are used by humans to obtain food or fur raw materials.
From a medical and sanitary point of view, the study of populations of small rodents - carriers of the causative agent of a dangerous disease for humans - plague is practically significant.
AND artificial selection lies the hereditary variability of organisms. As a result natural selection new forms of living beings are created - species, and through artificial selection - new varieties of plants and breeds of animals.
Artificial selection - a method of selection carried out by humans to create breeds of animals and plant varieties. The breeder selects individuals with advantageous traits and discards the rest. Breeds and varieties created through artificial selection can only exist thanks to human care, in wildlife they die. Artificial selection arose quite recently - from the time when man began to breed domestic animals and engage in agriculture. The selection of individuals with hereditary changes necessary for humans leads to the creation of completely new organisms that have never existed in nature before. These forms have characteristics and properties that suit human interests.
Artificial selection can be either spontaneous (unconscious) or methodical (mass or individual). The book on artificial selection summarizes thousands of years of human practice, and this doctrine has become the theoretical basis of modern selection.
Darwin believed that practitioners knew well how to obtain new breeds of domestic animals and varieties of cultivated plants, so he considered first the causes of breeds and varieties, and then species in a state of nature, believing that with this approach his ideas would be more revealing. By the 40s of the last century, a large number of large breeds were known cattle(dairy, meat, meat and dairy), horses (draft horses, racing horses), pigs, dogs, and also chickens. The number of varieties of wheat exceeded 300, grapes - 1000. Breeds and varieties belonging to the same species are often so different from each other that they can be mistaken for different species. Each breed or each variety, according to its characteristics, always meets the interests of the person for the sake of which he breeds them. Many supporters of the doctrine of constancy and immutability of species believed that each breed, each variety originated from a separate wild species. Darwin thoroughly came to the conclusion that man himself created all their diversity, as well as varieties of cultivated plants, changing in different directions one or several ancestral wild species.
Selection– a science that develops the theory and methods of breeding and improving animal breeds, plant varieties and strains of microorganisms. Selection is guided by the will of man. The theoretical foundations of selection are theory, genetics, molecular biology, economics, agricultural geography.
Breeding methods, their essence:
1. Mass selection – selection of a group of individuals possessing the desired characteristics (usually used repeatedly over a number of generations).
2. Individual selection– selection of individual individuals with the desired characteristics. Most suitable for animals and self-pollinating plants.
3. Interlinear - crossing two pure lines to obtain heterosis (heterosis is a phenomenon of very high viability in the first hybrid generation)
4. Distant hybridization– crossing of non-closely related forms and even different species. Used to obtain unusual combinations of genes for subsequent selection.
5. Polyploidy - an increase in the number of chromosome sets. Used in plant breeding to increase productivity and overcome infertility during interspecific crossing.
6. Cell engineering– growing cells outside the body (in tissue culture). Allows the passage of somatic (non-reproductive) cells.
7. engineering (artificial rearrangement of the genome. Allows the insertion of genes of another species into organisms of one species.
Selection is the science of improving existing and developing new breeds of animals, plant varieties, as well as practical human activities in these areas.
Modern breeding uses various methods. The main ones:
Study of the diversity of species, breeds and varieties existing in nature to use them as source material for selection;
Artificial selection of individuals with characteristics important to the breeder;
One of the main methods of selection is artificial selection, which involves the preservation and reproduction of organisms with traits that are valuable and useful to humans. Usually two types of artificial selection are used. Mass selection is carried out without taking into account the genotype of organisms, only according to external characteristics, i.e. based on phenotype, so the selected organisms are genetically heterogeneous. The mass selection method always requires repeated selection and is slow. Individual selection involves studying the genotype of parental organisms, analyzing offspring, conducting inbreeding and obtaining pure lines characterized by genetic homogeneity.
Artificial production of mutations by exposure to mutagenic factors;
Factors whose impact on the body leads to mutations are called mutagens. Mutagens are usually divided into three groups. Physical and chemical mutagens are used to artificially produce mutations.
Name of mutagens group:
A) Physical X-rays, gamma rays, ultraviolet radiation, high and low temperatures, etc.
B) Chemical Salts of heavy metals, alkaloids, foreign DNA and RNA, analogues of nitrogenous bases of nucleic acids, many alkylating compounds, etc.
B) Biological Viruses, bacteria
Induced mutagenesis is of great importance because it makes it possible to create valuable starting material for breeding, and also reveals ways to create means of protecting humans from the action of mutagenic factors.
Hybridization;
In modern breeding, hybridization (from the Greek hybris - cross) is widely used - natural or artificial crossing of individuals that differ in their characteristics and belong to different varieties, breeds, strains, species. Several types of crossing are used, including related and unrelated:
1. Inbreeding, or inbreeding (in cross-pollinated plants - forced self-pollination). Inbreeding results in offspring becoming homozygous, i.e. the degree of homozygous organisms increases. This is how pure lines of organisms are bred, which are widely used in breeding. With further crossing of individuals of two pure lines, one of which is homozygous for dominant genes, and the other for recessive genes, the first generation F1 hybrids are often superior to the original parent organisms in a number of traits - productivity and viability can sharply increase. In plant and animal breeding, this phenomenon occupies a special place and is called hybrid vigor, or heterosis. However, in subsequent generations, heterosis decreases and degeneration of the descendants is observed, so in practice only F1 hybrids are usually used. This is due to the fact that descendants increasingly begin to accumulate and manifest recessive mutations.
2. Unrelated crossing, or outbreeding. Organisms belonging to different lines within a variety (or breed), to different varieties (or breeds), to different species or even genera are crossed. In the last two cases we are talking about distant hybridization. Crossing organisms belonging to different species and especially genera is extremely difficult, because parent organisms differ in genetic material, physiological or morphological characteristics. Very often, such crossing leads to the formation of sterile (i.e., not producing offspring) hybrids. This is due to the fact that in a hybrid organism there are parental chromosomes that are so dissimilar from each other morphologically, and often in number, that they are not capable of conjugation; this leads to disturbances in the process of meiosis, and, consequently, normal germ cells are not formed ( gametes). However, the ability of plants to reproduce vegetatively, as well as the development of special methods for overcoming infertility in distant hybrids, in some cases makes it possible to form new forms that have certain valuable qualities characteristic of different species. The rapid development of new research methods in genetics, the expansion and deepening of our ideas about the structure and laws of organization of the hereditary apparatus of the cell have led to the creation and development of fundamentally new methods. New concepts and directions of modern genetics were born: cellular, chromosome engineering and genetic engineering. At the same time, the fundamental difference between these methods and those traditionally used in breeding lies in the targeted, and not random, expansion of the boundaries of genotype variability, in the planned diversity of the source material for breeding. These modern methods have so far found greater use in plant breeding. Cellular engineering involves the cultivation of individual cells or tissues in special artificial media. It has been shown that if you take pieces of tissue or individual cells from different organs, say, plants, although this is also possible in animals, and transplant them onto special media containing mineral salts, amino acids, hormones and other nutritional components, then they are able to grow. This means that in such tissues and cells isolated from the body, cell division continues. But the most important and interesting thing turned out to be that individual plant cells (unlike animal cells) under such artificial conditions have totipotency, i.e. capable of regenerating (forming) full-fledged plants. This ability was used for selection in different directions.
The second newest method of cell selection in plants, which has already given a huge effect, is the method of haploids (organisms with a halved number of chromosomes, in which in the nuclei of cells from each pair of homologous chromosomes, characteristic of diploids, only one chromosome is present.) For example, if corn is diploid Plants have 10 pairs of chromosomes (20 in total), while haploid plants have only 10 chromosomes. Gametes, including male ones (pollen grains), have a haploid set of chromosomes. This fact was used to obtain haploid plants.
A method has now been developed for germinating pollen grains on artificial nutrient media in test tubes and obtaining full-fledged haploid plants from them. It is based on hybridization, which results in heterozygous organisms, and then long-term homozygotization until the eighth generation, i.e. obtaining stable non-fissionable forms. It takes more than 10 years to create a variety using this method. With the help of haploids, this period can be reduced by 2 times. To do this, hybrids are obtained, pollen is taken from them, haploid plants are regenerated from it on nutrient media in test tubes, and then the number of their chromosomes is doubled and completely homozygous diploid plants are immediately obtained. This whole procedure takes 2-3 years instead of 6-8 years. Since we take pollen from hybrid plants and immediately obtain homozygous diploid plants through haploid plants, all that remains is to evaluate them and then propagate them better.
Chromosome engineering. At the moment, it is associated primarily with the possibilities of substituting (replacing) individual chromosomes in plants or adding new ones. It is known that in the cells of every diploid organism there are pairs of homologous chromosomes. Such an organism is called disomic. If in any pair of chromosomes there remains one homologous chromosome, then the result is monosomic. When a third homologous chromosome is added, a trisomic occurs, and when one pair of homologous chromosomes is missing in the genome, a nullisomic occurs. Such manipulations with chromosomes make it possible to replace one or both homologous chromosomes, say, of one wheat variety with the same pair of chromosomes, but from a different variety. Thus, he can replace one trait that seems weak in a given variety with the same, but stronger trait from another variety. Thus, he is approaching the creation of an “ideal” variety, in which all useful characteristics will be expressed to the maximum extent. The same goal is pursued by the technique of replacing individual chromosomes of one species with chromosomes of another species, similar in origin.
Genetic Engineering. Genetic engineering is usually understood as the artificial transfer of desired genes from one type of living organism (bacteria, animals, plants) to another species, often very distant in origin. To carry out gene transfer (or transgenesis), the following complex operations must be performed:
isolation from bacterial, animal or plant cells of those genes that are intended for transfer. Sometimes this operation is replaced by artificial synthesis of the necessary genes, if this turns out to be possible;
creation of special genetic constructs (vectors), in which the intended genes will be introduced into the genome of another species. Such constructs, in addition to the gene itself, must contain everything necessary to control its operation (promoters, terminators) and “reporter” genes, which will report that the transfer has been successfully completed; the introduction of genetic vectors first into a cell, and then into the genome of another species and the cultivation of modified cells into whole organisms (regeneration). Plants and animals whose genome is changed as a result of such genetic engineering operations are called transgenic plants or animals.
Topic 3.3. Genetics and selection.
Task 13. Genetics – theoretical basis selection. Teachings of N.I. Vavilov about the centers of diversity and origin of cultivated plants. Basic selection methods.
Target: to form initial knowledge about selection as a science, to determine its goals and objectives.
? 13.1 Compile a supporting summary of “Teachings of N.I. Vavilov on the centers of diversity and origin of cultivated plants"
Guidelines upon completion of the task:
When compiling a background outline, use the recommendations for doing independent work (section 4.6. Compiling a background outline. Free outline).
? 13.2 Complete the sentences by filling in the necessary terms and concepts instead of periods.
1. A set of methods for creating new varieties of plants, animal breeds and strains of microorganisms with characteristics needed by humans...
2. A set of cultivated plants of the same species, artificially created by man and characterized by certain hereditary characteristics -.....
3. Crossing of closely related individuals of plants and animals with a subsequent decrease in the viability of the resulting offspring is usually….
4. Genotypically homogeneous offspring obtained from a self-pollinating individual through selection are...
5. The powerful development of hybrids obtained by crossing pure lines is….
6. Crossing of individuals of the same species that are not directly related is...
7. Natural or artificial crossing of individuals belonging to different varieties, breeds, species, genera of plants or animals -….
Textbook Sivoglazov V.I. Biology: general biology. Basic level: textbook. for 10-11 grades. / IN AND. Sivoglazov, I.B. Agafonova, Zakharova E.T. -5th ed., - M.: Bustard, 2009. - §3.18, pp.176-180.
General biology: textbook for grades 10 – 11. total uch. / ed. D. K. Belyaeva, G. Dymshits – 6th ed. - M: Enlightenment, 2014 . §34-37, pp.129-142
Section 4. Evolutionary teaching.
Topic 4.1. Evolution theory.
Task 14. History of the development of evolutionary ideas. The significance of the works of C. Linnaeus, J.B. Lamarck in the development of evolutionary ideas in biology. Evolutionary doctrine of Charles Darwin.-1 hour.
Target: to form an understanding of the basic principles of Charles Darwin’s evolutionary theory; show the contribution of outstanding scientists to the development of biological science.
Assignment for independent extracurricular work:
? 14.1 Choose the correct statements:
1. Lamarck created the best artificial system.
2. Linnaeus believed that species exist and do not change.
3. Lamarck created the first evolutionary theory.
4. Lamarck believed that organisms change from simple to complex.
5. Linnaeus divided all animals into 5 classes.
6. Lamarck denied the variability of species.
7. Lamarck believed that characteristics acquired by species during life are inherited by descendants.
8. Linnaeus established the use of binary nomenclature for the species.
? 14.2 Fill out the table “Forms of natural selection”
? 14.3 Fill out the table “Comparison of natural and artificial selection”
"Introduction to general biology and ecology. Grade 9." A.A. Kamensky (GDZ)
Basic methods of selection of plants, animals and microorganisms (hybridization, selection, polyploidy, artificial mutagenesis)
Question 1. List the methods of selection work.
The main methods of selection include selection, hybridization, polyploidy, and artificial mutagenesis.
Plant breeding is based on artificial selection, when a person selects plants with traits that interest him. Until the XVI-XV centuries. selection occurred unconsciously, that is, a person, for example, selected the best, largest wheat seeds for sowing, without thinking that he was changing the plants in the direction he needed. Only in recent centuries has man, not yet knowing the laws of genetics, begun to use selection consciously and purposefully, crossing those plants that satisfied him to the greatest extent. Selection is also used in animal breeding.
To obtain new breeds and varieties of animals and plants, hybridization is used, crossing plants with desirable traits and then, selecting from the offspring those individuals that have beneficial features most strongly expressed. For example, one variety of wheat has a strong stem and is resistant to lodging, while another variety with a thin straw is not infected with stem rust. When plants of these two varieties are crossed, different combinations of traits appear in the offspring. But those plants are selected that both have a strong straw and do not suffer from stem rust. This is how a new variety is created. Hybridization is the natural or artificial crossing of individuals that differ in their characteristics and belong to different varieties, breeds, strains, and species. As a result of hybridization, hybrids are obtained. Hybrids are formed by combining the hereditary material of genotypically different organisms and are characterized by new characteristics or new combinations of them. Due to the difficulties in producing mass offspring from a pair of parents with the right person In the selection of animals, closely related crossing, or inbreeding, is used (English, in - in, inside; breeding - breeding), in which individuals from the same litter are crossed with each other or parent individuals are crossed with their own offspring. However, with inbreeding, there is a high probability of transferring any unfavorable recessive alleles to a homozygous state. As is known, mutations, in particular unfavorable ones, are usually recessive and rarely appear in the phenotype, but with inbreeding, such mutant genes will become homozygous and the unfavorable trait will appear. To eliminate the adverse effects of inbreeding, they use outbreeding(English out - outside; breeding - breeding) - crossing unrelated forms of the same species. In this case, there should be no common ancestors in the next 4-6 generations.
In all cases of hybridization, careful individual selection of producers is carried out for the next stages of selection. To take into account the nature of inheritance of traits, breeding farms maintain special stud books. The process of obtaining new breeds of animals is slow; It is believed that it takes at least 30-40 years to obtain a new breed, for example, cows. When breeding domestic animals, it is important to determine in advance the hereditary qualities of male producers based on traits that are not phenotypically manifested in them. Such signs may be milkiness and fat content in bulls or egg production in roosters. For this purpose, a method is used to determine the given quality of a breeding animal by offspring: first, a few offspring are obtained and their productivity is compared with the maternal one and with the average productivity of a given breed of animal. If the productivity of females in the offspring turns out to be increased compared to these indicators in the breed, then a conclusion is drawn about the great value of the producer. This method is used in breeding breeding work. Breeding also involves crossing organisms belonging to different species or even genera. In these cases, distant hybridization takes place - a rather complex process, since organisms belonging to different species, and even more so to different genera, have different genetic material (the number and structure of chromosomes). Very often, such crossing leads to the formation of infertile (sterile) hybrids that do not produce offspring. However, thanks to the painstaking work of breeding scientists, intergeneric hybrids have been obtained that are capable of reproducing. For the first time G.D. managed to do this. Karpechenko when obtaining a cabbage-raspberry hybrid. As a result of distant hybridization, a new cultivated plant was obtained - triticale- a hybrid of wheat and rye (lat. Triticum wheat and Secale - rye). Distant hybridization is widely used in fruit growing. There are distant hybrids among animals.
Polyploidy- obtaining polyploids, i.e. organisms in which the number of chromosomes is increased two, three or more times. Experimental polyploidy is widely used in plant breeding, since polyploids are characterized by rapid growth, large size and high yield. The phenomenon of polyploidy is based on the following reasons: each type of living organism has a strictly defined set of chromosomes. In germ cells, all chromosomes are different. This set is called haploid and is designated by the letter p. Cells of the body (somatic) usually contain a double set of chromosomes, called diploid (2n). If the chromosomes that have doubled during division do not separate into daughter cells, but remain in one nucleus, then a phenomenon of a multiple increase in the number of chromosomes occurs, called polyploidy. In agricultural practice, triploid sugar beets, tetraploid clover, rye and durum wheat, as well as hexaploid bread wheat are widely used. Artificial polyploids are obtained using chemicals that destroy the spindle, as a result of which the duplicated chromosomes cannot separate, remaining in one nucleus. One such substance is colchicine. The use of colchicine to produce artificial polyploids is one example of artificial mutagenesis used in plant breeding.
Artificial mutagenesis- a selection method based on the effect on organisms of mutagens that cause various mutations. Through artificial mutagenesis and subsequent selection of mutants, new high-yielding varieties of barley and wheat were obtained. Using the same methods, it was possible to obtain new strains of fungi that secrete tens of times more antibiotics than the original forms. Currently, more than 250 varieties of agricultural plants created using physical and chemical mutagenesis are cultivated in the world. These are varieties of corn, barley, soybeans, rice, tomatoes, sunflowers, cotton, and ornamental plants.
The technology of obtaining substances necessary for humans from living cells or with their help is called biotechnology. Most often, bacteria, fungi, and algae are used for biotechnology. These organisms are relatively unpretentious, multiply very quickly and are capable of releasing substances used by humans in various areas of the economy. Biotechnology is used in the food industry, medicine, nature conservation, etc. Vitamins, hormones, antibiotics, etc. are obtained with the help of bacteria and fungi. To date, new forms of bacteria have been obtained that can destroy petroleum products that pollute environment. Basic methods of biotechnology: cell engineering and genetic engineering. Cellular engineering is the cultivation of cells of an organism on artificial nutrient media, where these cells multiply, grow and secrete substances necessary for humans. For example, attempts are being made to grow a culture of endocrine gland cells to obtain hormones. The essence of genetic engineering is that a gene or group of genes from another organism is inserted into an organism (usually prokaryotic). As a result, it is possible to force a microorganism's cell to synthesize proteins that it could not produce before. Attempts are being made to transfer genes responsible for nitrogen fixation in nitrogen-fixing bacteria to other soil microorganisms. At the same time, the soil will receive from the air large quantities nitrogen, which will make nitrogenous fertilizers unnecessary. Artificial mutants of intestinal microbes have been obtained, in which the gene for insulin is built in, a pancreatic hormone vital for people with diabetes.
Question 2. How does mass selection differ from individual selection?
Mass selection is characterized by the fact that it is carried out only by phenotype, i.e. taking into account only the totality of the characteristics of the organism. Individuals with the desired characteristics are taken from the offspring and again crossed with each other. Mass selection is usually used for cross-pollinated plants and animals. This selection is aimed at maintaining a given breed or a certain variety at a given economic level.
In individual selection, a single individual is selected and through subsequent self-pollination in plants or closely related crossings in animals, pure lines are bred. Pure lines - groups of genetically homogeneous (homozygous) organisms - are valuable breeding material.
Question 3. What is heterosis?
Heterosis is manifested in the fact that hybrids have outstanding qualities (greater height, weight, resistance to diseases, etc.) compared to the parent forms. If cross-pollination is carried out between different “pure” plant lines, then in some cases the result is high-yielding hybrids that have the properties desired by the breeder. This method of interline hybridization often leads to the effect of heterosis: first-generation hybrids have high yields and resistance to adverse influences. Heterosis is characteristic of first-generation hybrids, which are obtained by crossing not only different lines, but also different varieties and even species. Unfortunately, the effect of heterotic power is strong only in the first hybrid generation, and gradually decreases in subsequent generations.
The main reason for heterosis is the elimination of the harmful manifestations of accumulated recessive genes in hybrids. Another reason is the combination of dominant genes of parental individuals in hybrids and the mutual strengthening of their effects.
