Polyploidy (from the Greek. polyploos - iterative and eidos - view) - fold increase in the number of sets of chromosomes. Single or haploid (and), set in higher plants and animals are represented in germ cells (see).
When sexual process after fertilization, i.e. the merger of two gametes (see), there is a new state with a double, or diploid (2n), set of chromosomes (see), passed the most somatic cells of a multicellular organism and representing for them norm.
Basically, himself sexual process gives the merger of two sets, the first stage of polyploidy, however, in the case of higher organisms by polyploidy is called a higher degree of multiplication, i.e. sets: triploid (RFP), tetraploid (4n), hexaploid (6n), etc.
Polyploidy special role in the processes of normal differentiation of certain cells in the individual development (ontogenesis) higher plants and animals, including humans. In addition, P. matters and in the processes of regeneration.
It should be noted the polyploidy observed in pathological conditions (growth of malignant neoplasms).
The extremely high value of P. in the formation of new species of plants. Closely related species of plants of one kind are often placed in the so-called polyploid series (wheat with 14 or 28, or 42 chromosomes and others). Morphological and physiological benefits of polyploid species enable them sometimes to colonize new areas that are inaccessible due to the harsh conditions for other species. It is found that in breeding of agricultural plants persons, unaware of the fact, for centuries led artificial selection polyploid forms, which now receive the bulk of food and fodder protein, fat and carbohydrates. Development of experimental method of creating polypoids already introduced some of them in the agricultural practice (triploid sugar beet, pepper mint, and others).
Prospective method of obtaining polyploid forms is often combined with artificial hybridization. Polyploidy is the only method of overcoming infertility hybrids by crossing distant species.
In the evolution of animals polyploidy has not received such values as in plants. This, apparently, was hampered by a complex mechanism of sex determination (see) in animals. However, where this barrier is removed, where parthenogenetic reproduction, appeared polyploid species, won more or less extensive areas.
Cases of spontaneous polyploidy in animals are observed as well as in plants; mastered and receive them in the experiment. This raises questions about their practical use. First steps are already made in our country C. L. Astaurov, received a breeding polypoids silkworm. Individual cases of P. detected in humans.