From Big Medical Encyclopedia

TRANSLOCATION (Latin trans-through + locatio placement) — restructuring of chromosomes or result of movement of a segment (segments) of chromosomes in chromosomal complement. T. can arise in a chromosome (chromosomal T.), in a chromatid (chromatid T.) and in subunit of a chromatid (polukhromatpdny T.).

Distinguish the following types of chromosomal

T. V of N at t r and x r about m about with about m of N and I am t r and N with l about to and c and I, pl shift, can be vnutrshtlechevy (movement of a segment of a chromosome within one her shoulder) and interhumeral (movement of a segment from one shoulder in other shoulder of the same chromosome).

M e x r about m about with about m of N and I am t r and nanosecond the location includes a transposition and reciprocal T. Transpozition is a transfer of a segment of one chromosome in another. The segment can be transferred within couple of homologous chromosomes (see) pl to be inserted into a heterological chromosome; in this case T. call an insertional insert, or an inser-tion. If the segment of one chromosome is postponed to the end of other chromosome, then T. call terminal (trailer).

In reciprocal T. call exchange of segments between heterological chromosomes. She is asymmetric and symmetric. Asymmetric reciprocal T. the centromere (atsentrichesky), and in connection of two fragments with centromeres consists in connection of two fragments of chromosomes, free of. As a result of such T. two products of exchange of segments are formed: atsentricheskiya, without centromeres, and dicentric, with two centromeres. Symmetric reciprocal T. consists in exchange of atsentrichesky fragments of geterologich-ny chromosomes or their whole shoulders. To symmetric T. nek-ry specific types T carry N., e.g. merges centromere, or robertsonovsky T., therefore there is an association of long shoulders of acrocentric chromosomes (a centromere is not in the center) to formation of a metatsentri-chesky chromosome, a centromere a cut is located in the middle. Reverse of transformation of one metacent-richesky chromosome with long shoulders and another — with short in two acrocentric chromosomes (so-called dissociation) when the rupture of one chromosome occurs close centromeres, and a rupture of the second chromosome — on its distal end (so-called tandem merges), is also referred to symmetric T.

For an explanation of origins of T. two hypotheses are offered. According to a hypothesis «a gap — recovery» primary damage is a gap therefore there is possible a transfer of chromosomal fragments and their reunion in other order. According to a hypothesis of «exchanges» of T. is result of the exchanges happening on certain labile websites (sites) after contact of chromosomes.

All listed types T. occur at the person and can mention any of his chromosomes. In gonads of translocational heterozygotes at meiosis (see) there are gametes of two types: balanced and unbalanced (see Gametes). If translocational chromosomes jointly depart to the same pole, and not trans locational — to another, then both types of gametes receive full ranges of genes, i.e. the balanced gametes are formed. If distribution of chromosomes happens in other way, then gametes turn out unbalanced. On average the number of the balanced and unbalanced gametes at translocational heterozygotes is approximately identical, i.e. about a half of zygotes (see the Zygote) will normally develop, and other half will die (a so-called semisteril N an awn). In case of incoincident (discordant) orientation a centromere in meiosis translocational heterozygotes can have gametes with n — 1 and gs +1 chromosomal complements (see Chromosomal complement). As a result mono-somnye and trisomny zygotes can form, to-rye depending on extent of disturbance of balance, specifics of the mentioned genes and chromosomes can stop the development on early reduction stages or lead to an abortion or a still birth. The embryo with such chromosomal complement can sometimes develop in a viable fruit, but at the birth at children note more or less heavy malformations. Frequency of emergence of T. raises at influence of mutagen factors.

Bibliography: Bochkov N. P., Chromosomes of the person and radiation, M., 1971; it e, Genetics of the person, Heredity and pathology, page 227, M., 1978; 3 ah and r about in A. F. Chromosomes of the person, page 58, M., 1977; Zakharov A. F., etc. Chromosomes of the person, Atlas, M., 1982; Hereditary diseases, under the editorship of JI. O. Badalyana, page 375, Tashkent, 1980; The Teratology of the person, under the editorship of G. I. La-zyuk, page, 262, M., 1979. V. A. Mglinets.