From Big Medical Encyclopedia

RECOMBINATION ANALYSIS — a method of a research of the structurally functional organization of genetic material by results of a recombination of ancestral features, chromosomes, genes, alleles; main method of the genetic, in particular hybridological, analysis. Purpose P. and. consists in definition of localization of the genes responsible for manifestation of the studied signs, and in nek-ry cases in definition of their thin structure. In to genetics (see) R. and. is one of the main methods giving the chance to find out the organization of this or that genome biol. look. River and. allows to establish identity, an associativity or independence from each other of mechanisms of genetic control of important signs and properties of organisms that is a basis for rational forecasting of emergence of such signs and properties and their manifestation at descendants. In medical genetics it is necessary for calculation of probability of emergence (transfer) of a hereditary disease and, respectively, for its prevention (see. Hereditary diseases ). In selection of animals, plants and R.'s microorganisms and. it is necessary for purposeful creation of the genotypes providing emergence of organisms with required combinations of signs and properties.

Philosophy of R. and. the full quantitative account in posterity of hybrids of all combinations of the analyzed (tested) sign with others is (or to others) ancestral features, rules of inheritance to-rykh are known and to-rye are used as genetic markers. In genetics of eukaryotes the main condition for R.'s carrying out and. use of organisms of genetically marked constant lines is (usually inbredny). As genetic markers can be used morfol., fiziol. or bio-chemical the signs controlled by genes with the established localization and stable manifestation, i.e. genes with full penetrance (see. Penetrance of a gene ) and not varying expressivity (see. Expressivity of a gene ) not only in datum lines, but also at hybrids and in their posterity. Existence in karyotype (see) eukaryotes more than one couple of chromosomes demand use in R. and. it is multiple the marked lines, at to-rykh each of couples of chromosomes (linkage groups) bears at least one genetic marker. At low-chromosomal types sometimes it is possible to manage one combined line. At multichromosomal types the impossibility of the simultaneous account at one individual of a large number of signs usually causes the necessity of creation of set of lines testers. There are options P. and., based on use of testerny lines both with dominant, and with recessive genetic markers.

In genetics of prokariot (bacteria, viruses) R. and. also the gaploidnost of these organisms is based on receiving recombinants on the studied and marker signs, however (see. Chromosomal complement ) and lack of heterozygosity from them is demanded by uses of specific methods of receiving and assessment of the recombinants other than usual hybridization for bisexual diploid eukaryotes.

First stage P. and. at eukaryotes establishment of accessory of the gene controlling the studied sign to one of linkage groups of genes, i.e. to a certain chromosome is. Traditionally it becomes by crossing (or series of crossings) representatives of an ispytuyemy form of organisms with individuals of lines testers for identification of those genetic markers, in combinations with to-rymi the rule of an independent combination of signs is violated (see. Mendel laws ). In to genetics of the person (see) such research represents systematic search probands (see) with the set combinations of ancestral features and the subsequent genealogical studying of inheritance of these combinations in families of probands (see. Genealogical method ). With development of methods of the distant hybridization of somatic cells in culture (see. Genetics of somatic cells ) and studying of their biochemical phenotype there was an opportunity to determine belonging of this or that gene to a certain chromosome by correlation between preservation of this chromosome in a karyotype of a hybrid and manifestation of effects of the studied gene in the corresponding cells (or, on the contrary, on correlation of disappearance of this chromosome from a karyotype of a hybrid with disappearance of effect of the studied gene).

Second and main stage P. and. definition of situation (localization) of a gene on the corresponding chromosome is (see. Chromosomes ). Usually estimate frequencies recombinations (see) the studied gene with two genetic markers far remote from each other on this chromosome. Results of such analysis express as a percentage krossoverny gametes (a so-called morganida, unit of the card). Accumulation and synthesis of data on recombinational distances allows to build genetic maps of chromosomes (see. Chromosome map ). In genetics of the person determination of recombinational distances according to genealogical data is limited to rare occurrence of families, in to-rykh the studied combinations of the linked signs are inherited. Therefore methods of genetics of somatic cells give the main contribution to exact mapping of genes of the person. Especially effectively at the same time deletsionny mapping (see. Deletion ): if at a karyotype there is a usual chromosome bearing the studied gene, and its homolog contains deletion of the same localization, as this gene, then a phenotype of an individual and inheritance of the analyzed sign will follow the consistent patterns determined for a gemizigotny condition of genes. Drawing up genetic maps by deletsionny mapping demands use of many cellular lines with divisions on the most different sites of different chromosomes of a genome. Cellular lines usually receive from patients with the chromosomal diseases caused by chromosomal deletions. Since it is a little people with such diseases, broad use of mapping of genes by means of deletions is impossible. Besides, by such method it is possible to map only those genes, for to-rykh their manifestations at the cellular level are known.

In genetics of the person of an opportunity R. and. are limited so far to establishment of localization of genes within a kariologicheska (by means of methods of differential coloring) the identified segments of the chromosomes containing on several tens of genes. R.'s possibilities and. in experimental genetics is much wider: the research of posterity of the corresponding hybrids at analysis of several thousand individuals allows to map the provision of genes to within the 100-th shares of a morganida that approximately corresponds to separate genetic loci. If to increase number of the studied individuals in the corresponding types of crossings to several tens of thousands, then, except products of an intergene recombination — a crossing-over, it is possible to find also products of much more rare intragenic recombinations (see), allowing to investigate fine structure of separate genetic loci. There are separate examples of such thin R. and. for eukaryotes (a drosophila, neurodisputes, yeast), but especially great success is achieved in studying by means of R. and. the internal organization of genes at bacteria, viruses and bacteriophages.

See also Genetic analysis .

Bibliography: Gershenzon S. M. Fundamentals of modern genetics, page 93, Kiev, 1979; To at sh e in V. V. Mechanisms of a genetic recombination, JI., 1971, bibliogr.; Serebrovsky A. S. Genetic analysis, M., 1970; Human gene mapping, ed. by D. Bergsma, v. 13, p. 1, 1974, v. 14, p. 162, 1975; v. 16, p. 1, * 1976; v. 22, p. 1, 1978; v. 25, p. 2, N. Y., 1979.

V. I. Ivanov.