GAMETES

From Big Medical Encyclopedia

GAMETES (Greek gametes the husband, the spouse) — specialized sex cells at the organisms breeding sexually which provide at the merge in the course of fertilization transfer and combination of the gene program of parent individuals for development of signs of a new organism.

At all metaphytes mature G. develop in gonads — gonads (men's — seed plants and women's — ovaries) from unripe zachatkovy cells — gametocytes. In the course of growth and G.'s maturing — gametogenesis (see) diploid (usual double) chromosome number in kernels of gametocytes is reduced as a result meiosis (see) to haploid (twice smaller). Mature G. of a gaploidna. At formation of a zygote as a result of G.'s merge the diploid chromosome number characteristic of cells of a new organism is recovered. Male and female G. considerably differ. At the vast majority of organisms the heterogamy takes place: spermatozoa (microgametes) contain a small amount of cytoplasm, the small kernel, «tail» (burn down) and have physical activity; ova (macrogamete) have a large amount of cytoplasm, the big sizes and are not capable to active movement.

Gametes of the person (scheme); and and — men's (spermatozoa): and — a view from a plane surface of a head; 1 — a head; 2 — a neck; 3 — «tail»; — a view from a side surface of a head; in — female (ovum) at the time of the II division of meiosis: 1 — chromosomes; 2 — a napravitelny little body; 3 — a noncellular secretory layer (a transparent cover); 4 — the remains of follicular cells.

At some organisms (roundworms, the majority of arthropods) male G. (spermiya) have no organella of movement and move by formation of cellular outgrowths — pseudopodiums. In some cases an active role in capture motionless spermiyev is played by ova. At vegetable organisms (green and brown seaweed) both the male and female G. differing in the sizes have mobility (women's — macrogametes). At the lowest mushrooms and cabbage-weeds of G. are not distinguishable morphologically (isogamy).

The heterogamy — significant differences of G. on structure (fig.) and a role in the course of fertilization is characteristic of the person and the highest animals. Cytoplasm of ova is rich with the cytoplasmatic DNA and RNA, free nucleotides, proteins and other substances necessary for ensuring development of a zygote. Thus, spermatozoa generally bear nuclear genetic information, ova — nuclear and cytoplasmatic genetic information plus the intracellular environment for the first stages of its implementation at development of a new organism.

At the elementary unicells at sexual process function G. is performed by the individuals in some cases undergoing at the same time morfo-fiziol. changes (see. Protozoa ). Sexual process at some inferior plants and the elementary animals proceeds without G.'s participation — in the first case physiologically heterosexual body parts or somatic cells merge, in the second there is an exchange of a part of kernels (micronucleus) at temporary contact (conjugation) of two adult individuals (see. Infusorians ).


Bibliography: Petten B. M. Embryology of the person, the lane with English, M., 1959; The Guide to cytology, under the editorship of A.S. Troshin, t. 2, page 390, M. — L., 1966; Austin C. H. The mammalian egg, Springfield, 1961.

Yu. F. Bogdanov.

Яндекс.Метрика