The basis for the success of any selection work -genetic diversity of material and methods of selection. The use of such raw materials makes it possible to obtain new hybrids and varieties, with a wide variety of characteristics and properties. Foundations of selection were laid by the most famous scientists of the world:
- H. Mendel (laid the foundations of genetics, discovered the principle of discreteness);
- Charles Darwin (founded the theory of origin, conducted many experiments on crossing);
- T. Fairchild (in 1717 received the first artificial carnivorous hybrids);
- II Gerasimov (discovered the change in the number of nuclei and hereditary changes associated with the mutation);
- MF Ivanov (introduced genetic principles in the selection of animals);
- N. K. Koltsov (created the basis for molecular genetics).
- NI Vavilov (discovered the law of homological series);
- IV Michurin (brought out a lot of fruit hybrids).
The main methods of plant and animal breeding wereDeveloped on the basis of all previous discoveries and improved to this day. Breeders in their work use different methods of selection: inbreeding, artificial mutagenesis, polyploidy, remote hybridization. Below are the most commonly used methods of breeding new plants and breeds of animals.
Basic 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 homogeneity of the variety, individual selection is used, in the course of which by self-pollination the generation of offspring from a single individual possessing all the best attributes is achieved. The disadvantage of this method is that often unfavorable manifestations of recessive genes are observed. The main reason for this is the transition of a large number of genes into a homozygous state. Over time, the accumulation of recessive mutant genes passing into a homozygous state can cause adverse hereditary changes. In natural conditions in a self-pollinated plant, recessive genes become homozygous, and such a plant quickly dies.
When using the self-pollination method, oftenyield decreases. 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 interlinear hybridization. The hybrids of the first generation have the highest yield. In this case, a known effect of heterosis is observed, according to which powerful hybrids are produced by crossing "clean" lines. They are resistant to adverse effects, because they removed the harmful effects of recessive genes, and the combination of strong dominant genes of parental plants enhances the effect.
Often in the selection of different plantsExperimental polyploidy is used. The plants obtained in this way are large in size, yield a good harvest and grow rapidly. Artificial polyploids are produced under the influence of chemical substances that destroy the spindle of division. As a result, doubled chromosomes remain in the same nucleus.
New varieties are derived and with the help of artificialmutagenesis. The organism, which as a result of mutation has received new properties, has a weak viability, therefore at natural selection it is eliminated. For the selection and evolution of new varieties and breeds, rare individuals with neutral or favorable mutations are needed.
Methods of breeding animalsdiffer 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 crossing are carried out with certain goals, set by the breeder. All animals are evaluated not only by their appearance, but also by the quality of their offspring and their descent. Therefore, it is so important to know their pedigree. In breeding, two methods of crossing are most often used:
- Inbreeding (closely related) - crossed parents, sisters, brothers. This crossing can not be done indefinitely. It is used, as a rule, to improve the properties of the rock;
- Outbreeding (unrelated) - crossing of representatives of one or different breeds and strict selection of descendants with better properties.
Remote hybridization of animals is much less effective than plant hybridization. Such interspecific hybrids are often fruitless.
