The basis for the success of any breeding work is the genetic diversity of the material and breeding methods. The use of such starting materials allows to obtain new hybrids and varieties, with a wide variety of characteristics and properties. The basics of selection were laid by the most famous scientists of the world:
- G. Mendel (laid the foundations of genetics, discovered the principle of discreteness);
- C. Darwin (founded the theory of origin, conducted many experiments on crossbreeding);
- T. Fairchild (in 1717 received the first artificial hybrids of carnations);
- I. I. Gerasimov (discovered a change in the number of nuclei and hereditary changes associated with a mutation);
- M.F. Ivanov (introduced genetic principles into animal breeding) ;
- N.K. Koltsov (created the basis for molecular genetics).
- N.I. Vavilov (discovered the law of homological series);
- I.V. Michurin (bred a lot of fruit hybrids).
The basic methods of plant and animal breeding were developed on the basis of all previous discoveries and are still being improved. Breeders use various breeding methods in their work: inbreeding, artificial mutagenesis, polyploidy, distant hybridization. Below are the most commonly used methods of breeding new plants and animal breeds.
The main methods of plant breeding: hybridization and selection. Cross-pollinated plants are selected by mass selection of those individuals that have the desired properties. To obtain the purest lines, that is, the genetic uniformity of the variety, individual selection is used, during which self-pollination is used to obtain offspring from the only individual that has all the best features. The disadvantage of this method is that in this case, adverse manifestations of recessive genes are often observed . The main reason for this is the transition of a large number of genes to the state of homozygous. Over time, the accumulation of recessive mutant genes, turning into a homozygous state, can cause adverse hereditary changes. Under natural conditions, in a self-pollinated plant, recessive genes become homozygous, and such a plant quickly dies.
When using the self-pollination method, productivity is often reduced. To increase it, cross-pollination of different self-pollinating plant lines is carried out and high-yielding hybrids are obtained. Such selection methods are called interline hybridization. Hybrids of the first generation have the highest productivity. At the same time, a well-known effect of heterosis is observed, according to which when crossing βcleanβ lines powerful hybrids are obtained. They are resistant to adverse effects, since they eliminated the harmful effects of recessive genes, and the combination of strong dominant genes of the parent plants enhances the effect.
Experimental polyploidy is often used in the selection of various plants. Plants obtained in this way are large, give a good harvest and grow quickly. Artificial polyploids are obtained under the influence of chemicals that destroy the spindle of division. As a result, doubled chromosomes remain in the same nucleus.
New varieties are also bred using artificial mutagenesis. An organism that has received new properties as a result of mutation has a weak viability, therefore it is eliminated during natural selection . For breeding and evolution of new varieties and breeds, rare individuals with neutral or favorable mutations are needed.
Methods of animal breeding practically do not differ from the basic methods of plant breeding. Features of working with them - their sexual reproduction and small offspring. The selection of parents and the type of mating are carried out with specific goals set by the breeder. All animals receive an assessment not only by their external characteristics, but also by the quality of their offspring and their origin. Therefore, it is so important to know their pedigree. In breeding, 2 methods of crossing are most often used:
- inbreeding (closely related) - parents, sisters, brothers cross. Such a cross cannot be carried out endlessly. It is used, as a rule, to improve the properties of the breed;
- Outbreeding (unrelated) - crossing of representatives of one or different breeds and strict selection of offspring with the best properties.
Remote animal hybridization is significantly less effective than plant hybridization. Such interspecific hybrids are often sterile.