segregation in biology

From Big Medical Encyclopedia

SEGREGATION in biology (late lat. segregatio department) — allocation (vyshchepleniye) of any new base units of living matter (biocenoses, types, subspecies, populations, cells, kernels, chromosomes, genes, etc.) in the course of its development. S.'s processes are the cornerstone of organic evolution and proceed for a long time. In process ontogenesis (see) there is cytoplasmatic S. leading to emergence of distinctions in chemical structure and properties of different sites of cytoplasm of an oosperm, various groups of cells of an embryo, cells of the growing and growing old organism that is a basis of a cellular differentiation and a morphogenesis at germ (see), and also development organism (see) in the postembryonal period.

In to genetics (see) and molecular biology (see) S. it is accepted to call process of distribution (discrepancy) of elements of genetic material (chromatids, homologous chromosomes, genes, molecules DNA) in daughter cells. As a result of mitotic division of somatic cells of metaphytes (see. Mitosis ) there is S. controlled genetically of chromatids of each of chromosomes, i.e. so-called somatic S., edges leads to exact distribution in daughter cells of two copies of genetic material of maternal chromosomes (see). At hybridization of somatic cells there is a gradual loss of a part of chromosomes that received the name of a segregation of genomes. Formation of sex cells (gametes) is connected with S. of homologous (pair) chromosomes of a diploid mother cell in process meiosis (see). Accidental association of genetic material of haploid gametes at fertilization (see) leads to independent S. of genes of parent organisms and S. of the corresponding signs at posterity (see. Mendel laws ).

the Diagrammatic representation of a segregation of mutant chromosomes at bacteria: I and II — cycles of cellular division; And — a dominant allele; and — a recessive allele. The bacterial cell contains four identical nucleoids (homologous chromosomes), in each of which there is a dominant allele And. The mutation in one of chromosomes is resulted by a recessive allele and, because of suppression by a dominant allele But not capable to be shown phenotypical. After two cycles of cellular division there is a cell, all chromosomes a cut bear a gene and, and manifestation of the sign controlled by this gene becomes possible.

At prokariot (e.g., at bacteria) mechanisms C. of genetic material significantly differ from typical mechanisms of a mitosis and meiosis of the higher organisms. Process of replication of a bacterial chromosome (see Replication) is connected probably with its attachment to a certain site of a cellular membrane. Assume that S. of replicated chains of DNA of a chromosome occurs due to growth of the site of a cellular membrane, it is attached to Krom that leads to «drawing apart» two copies of genetic material and their hit in daughter cells. In the course of exchange of genetic material at bacteria partially diploid zygotes usually form (see. Conjugation at bacteria ). The subsequent recombination of endogenous and exogenous sites of genetic material (see. Recombination ) in such zygotes is followed by S. of these sites leading to formation of haploid recombinants (segregant). The page of genetic material of bacteria plays also important role in the mechanism of manifestation of recessive mutations (see. Mutation ). Because each bacterial cell in a phase of exponential growth (see. Bacteria ) usually contains several identical nucleoids (homologous chromosomes), recessive mutation in a gene of one of such chromosomes cannot receive immediate phenotypical manifestation (fig). However as a result of two subsequent cellular divisions S. of the chromosomal copies bringing dominant and recessive alleles of this gene to various daughter cells that leads to S. of a recessive character and a possibility of its phenotypical manifestation is possible.

Clarification of mechanisms C. of various taxonomical groups of live organisms (populations, subspecies, types, etc.) is important for understanding of common problems of organic evolution (see. Theory of evolution ) and for the solution of a number of practical problems of biology and medicine (questions of environmental control, a problem of evolution of activators infectious and parasitic diseases, etc.). Data on specific genetic mechanisms of cytoplasmatic S. in the course of ontogenesis of the person and the reasons of their disturbance are extremely important for the correct understanding of essence of various anomalies of development, malignant growth, a senilism and other phenomena connected with disturbance of normal processes of a differentiation, proliferation, migration, integration and death of cells and also during the planning to lay down. actions for correction of such disturbances. Various factors leading to disturbance of homologous chromosomes by normal S. at a gametogenesis are an origin chromosomal diseases (see) the person. The page of genes is the cornerstone of S. patol. the signs which are inherited among generations of a certain family. The analysis of family trees is based on S.'s studying genes (see. Genealogical method ) at hereditary diseases (see), their diagnosis and medicogenetic consultation (see. Medicogenetic consultation ). S.'s phenomenon of genomes in posterity of intergeneric hybrids of somatic cells is widely used during the mapping of genes of the person. Data on mechanisms C. of genetic material in cases of genetic exchange and a mutagenesis at bacteria are of interest in the analysis of ways of distribution of genes and plasmids (see), controlling medicinal stability of microorganisms (see), their virulent and other properties in populations of pathogenic and conditionally pathogenic bacteriums, in the analysis of formation of atypical forms of these organisms, etc.

Bibliography: N. P. Genetik's tanks of the person, M., 1978; Davidson E. Action of genes in a prematurity, the lane with English, M., 1972; Zussman M. Developmental biology, the lane with English, M., 1977; Mayr E. Populations, types and evolution, the lane with English, M., 1974; Physiological genetics, under the editorship of M. E. Lobashev and S. G. Inga-Vechtomov, D., 1976; X e y from U. Genetik of bacteria and bacteriophages, the lane with English, M., 1965.

V. P. Shchipkov.