From Big Medical Encyclopedia


chroma color, coloring + soma a body) — set of the chromosomes which are contained in any cell of an organism. X. the N for each species of plants and animals is constant on chromosome number, their sizes and a form.

X. the N of sexual and somatic cells is various. — gametes — contains in mature sex cells unary (haploid) X. N, the designated lat. a letter p in which each chromosome (see Chromosomes) is presented by one recombinant copy: a part of its genes occurs from mother, a part — from the father (see Meiosis, the Recombination). The zygote which is result of merge of men's and female mature sex cells and all cells of the organism developing from it (somatic cells) carry double (diploid) X. the N designated 2 items. To haploid X. the N return comes only in the course of maturing of sex cells in meiosis. Total number of chromosomes in haploid X. the N constantly is also called chromosomal number. At the person it is equal 23 (22 autosomes and one of gonosomes — X or Y).

For studying of X. N use cells in a meta phase of mitotic division (see the Mitosis) or in a pro-phase and metaphase of meiotic division. Polytene chromosomes (see Chromosomes) investigate in the period of interphase. For morphological studying of X. N apply light microscopy with use of drugs of integral chromosomes all the X. N, lying in one plane. On such drugs it is possible to receive by means of intravital impacts on chromosomes (radioisotopes, etc.) and special methods of their processing and coloring the versatile morphological and functional characteristic of X. N.

Set of morphological features full H.n. somatic cells at a stage of metaphase of cellular division the karyotype is designated by the term (see). In X. N of the person enter chromosomes of all three types: metacentric, submetacent-richesky and akrotsentrichesky. At standard uniform coloring by the main dyes, and also by means of differential coloring of a chromosome on length special metodakhm (

Q-, G-, R-, S-coloring, intravital inclusion of a 5-bromdezoksiuridin) all chromosomes of X. the N manages to divide into individual couples. For more exact detection of nature of restructurings of chromosomes at diagnosis of chromosomal diseases (see) try to subject to karyotyping chromosomes in a stage of prometaphase of cellular division when they are differentiated on bigger quantity of segments. X. the N can be investigated also in the cells which are exposed to meiotic divisions: in a pro-phase I and metaphase I and II of divisions. In a pro-phase I full of X. the N is the most available to the analysis at a stage of a pachytene when chromosomes of each couple thanks to a close prileganiye to each other (see Conjugation of chromosomes) form the uniform structure (bivalent) which is unevenly condensed on length. On number, a form and an order of an arrangement of sites of condensation (chromomeres) it is possible to distinguish individual bivalents. The analysis of morphology of individual bivalents helps identification of structural chromosomal reorganizations at a number of chromosomal diseases.

The most important purpose of studying of X. the N is clarification of gene structure of each chromosome with definition of localization of genes on its length — gene mapping of X. N (see. Chromosome map).

Genetic characteristic

of X. the N of the person is intensively developed in recent years and is far from end (e.g., on chromosomes of the person more than 500 genetic loci in autosomes are mapped by the end of 1983, 254 — in X-chromosome and 7 — in U-hromoso-me. All 22 autosomes of chromosomal complement are to a greater or lesser extent mapped. Existence of cytologic cards of chromosomes allows to localize a number of genes in certain segments on length of chromosomes.

Development of the molecular characteristic of X. the N of the person is a recent trend which develops on a joint of molecular genetics (see) and cytogenetics (see) also it is closely connected with genetic mapping of chromosomes. Its purpose consists in a research of features of DNA of individual chromosomes. Certain data on distribution on chromosomes of set of the DNA types with high repeatability of the nucleotide sequences are received. This DNA is localized in the heterochromatinic areas revealed at S-ok-raske.

Constancy of chromosome number in X. the N of this species at his certain representatives can be broken. This phenomenon is studied at many species of plants and animals, and also at the person (see the Mutation). Disturbances can concern frequency rate of haploid set — ploidy. They include polyploidies: triploidy (Zp), tetraploi-diya (4 p) and t:. All forms not multiple p changes of chromosome number in X. N combine the term an aneuploidy. Reduction of chromosome number carries the name of a gipoploidiya, increase — giperploidiya. Lack of one chromosome from couple call a monosomy, existence additional — a trisomy, during the loss of both homologous chromosomes of this couple speak about a nullisomiya. Quantitative changes of any type can take place in limited number of cells of this fabric and body. Such is a physiological polyploidy in hemopoietic, placental and nek-ry other fabrics. Different types of a polyploidy and an aneuploidy find in the majority of malignant tumors. Quantitative deviations in ploidy or number of individual chromosomes can be observed in all cells of an organism or in large part cells (see Mosaicism). Such numerical deviations can be the cornerstone of multiple inborn malformations (see. Chromosomal diseases).

Bibliography: B about with t about to To. and Sumner. A chromosome of an eukaryotic cell, the lane with English, M., 1981; B about the h to about in N. P, 3 ah and r about in A. F. and And in and N about in V. I. Meditsinskaya of the geneticist, M., 1984; Darlene -

of t about S.'s N of and JI and To at r L. F. Chromosomes, the lane with English, M., 1981, bibliogr.; 3 ah and r about in A. F. Chromosomes of the person (problem of the linear organization), M., 1977,

bibliogr.; 3 and x and r about in A. F., etc. Chromosomes of the person, Atlas, M., 1982, bibliogr.; Fundamentals of cytogenetics of the person, under the editorship of A. A. Prokofieva-Belgovskaya, M., 1969. A. F. Zakharov.