GAMETOGENESIS

From Big Medical Encyclopedia

GAMETOGENESIS (gametes + grech, genesis an origin) — process of education and development of sex cells. Genesis of men's sex cells is called spermatogenesis (see), women's — oogenesis (see). The general for these processes is change of four main stages (periods). The first stage — mitotic reproduction of primary sex cells — the gametogoniums containing a diploid set of chromosomes. The second — the growth of these cells which is most expressed in an oogenesis and consisting in accumulation of mass of the cytoplasm containing the substances necessary for development of a new organism and also in doubling of DNA (material of hereditary information) in chromosomes of kernels of the cells called already by gametocytes. The third stage — maturing gametes (see), i.e. transformation of gametocytes into the spermatids or ootida different from gametocytes as haploid (twice smaller) chromosome number, and a raznokachestvennost of genetic material in them. Basic process of this stage is meiosis (see) — two consecutive divisions of gametocytes which essence consists in a reduction (reduction) of chromosome number of the ripening gametes to haploid and in partial exchange of genetic material — conjugation and a crossing-over (cm; Conjugation of chromosomes , Recombination ). The fourth period — formation of mature gametes: formation of covers at ova and typical structure (a head, a neck, a tail) at spermatozoa. At female individuals of the highest animals and the person the first two stages proceed in ovaries, and maturing and formation — in pipes (oviducts). Is one of the basic processes defining genetic and fiziol, features of gametes and consequently, and features of development of a new organism. It is possible to consider one of stages of an ontogeny, i.e. primary — the pro-embryonal period ontogenesis (see). G.'s disturbance conducts to patol, to changes of gametes and serious consequences in the course of an ontogeny of an individual (see. Gametopathies ).


Bibliography: Pozhidayev E. A. Oogenesis of mammals, M., 1967, bibliogr.; It is equal to X. An oogenesis, the lane with English, M., 1964, bibliogr.; Robertis E., Novinsky V. and With F. A NPP. Cytobiology, the lane with English, M., 1973.

Yu. F. Bogdanov, V. N. Pavlova.

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