Heterosis in Animal Breeding
The selection process is based on artificial selection. Selecting for breeding the best animals, the most productive forms of plants or strains of microorganisms, a person fundamentally alters the wild ancestors. The doctrine of selection, created by C. Darwin, as well as knowledge about the variability and heredity of organisms, form the basis of the theory and practice of selection.
C. Darwin also noted that the material for selection is supplied by hereditary variability arising within animal breeds and plant varieties. Selection changes the trait only if the individuals that are selected are hereditarily diverse.
Selection and its creative role. At the first stages of domestication, a person used selection unconsciously, that is, without a conscious goal to change animals and plants in the right direction. He left only those animals that were able to exist and breed in captivity. Aggressive and cowardly animals either were destroyed, or were so depressed that they were not able to breed. Thus, a person unconsciously selected animals according to their behavior and changed them so much that wild animals became domestic animals, and some, for example, dogs, became friends of a person.
Of course, plants were also subjected to unconscious selection. For example, wild primitive forms of cereals are characterized by the fragility of an ear, which serves as a device for the distribution of seeds. Gathering a crop of plants at a certain time, a person conducted an unconscious selection for the strength of the spike rod, which became a characteristic sign of cultivated cereals.
In the early stages of the development of livestock and crop production, a person noticed that, as a rule, the best offspring are born from the best individuals, that is, those most satisfying their needs. Since that time, a person, not yet knowing the laws of heredity and not owning the theory of selection, began to use it consciously, leaving for further reproduction the organisms of animals or plants that are most satisfying to him. Such a conscious, methodological selection, carried out by man for many generations, led to a sharp change in a number of signs and properties of animals and plants, made them adapted to human needs and not like their wild ancestors. Thus, selection has created new forms of organisms. This is his creative role.
Assessment of hereditary qualities. The signs that interest the breeder are very diverse. The phenotypic variability of some of them is strongly determined by the diversity of genotypes and is relatively little dependent on living conditions. An example is the length of a sheep’s coat.