From Big Medical Encyclopedia

GENETIC ANALYSIS (grech, genetikos relating to an origin; analysis decomposition, a partition) — set of methods of studying of hereditary properties of organisms. The analysis of character of inheritance of characters among generations of organisms allows to obtain data on structure, a structure and functioning of the hereditary device of cells.

By means of G. and. two main types of tasks are solved: 1) the analysis of the nature of observed hereditary distinction in signs between two individuals (groups of individuals, populations, breeds, types), identification of number of the genes which are the cornerstone of this distinction, studying of properties of these genes, their couplings with other genes, their localization on the chromosome map; 2) perhaps complete description of a genotype of an individual (population, look).

First and obligatory stage G. and. clarification of the nature (hereditary or not hereditary) chosen for G. is and. sign. In genetics of animals, plants and microorganisms this issue is resolved by systematic closely related cultivation (see Inbreeding) or vegetative reproduction of the analyzed organisms in a lineage. In genetics of the person where systematic crossing is impossible, the hereditary nature of the interesting sign is proved by its family confinedness, and also high hit rate at monozygotic twins (see. Twin method). To prove the hereditary nature of the studied sign, or to define a share of a hereditary component in its emergence happens quite difficult, more precisely. It is caused first of all by the fact that communication between genes and signs controlled by them depends in most cases on cumulative influence genotypic, internal and the environment of an organism. Other factor influencing reliability of the conclusion about the hereditary nature of the studied sign is test-sensitivity, with the help to-rogo this sign is studied since the range of hereditary distinctions stretches from ultrastructural and small biochemical, changes in separate components of cells to makromorfo l. and fiziol, features of organisms. Therefore in G. and. use methods various biol, and medical disciplines. The general for G. and. any signs studying of patterns of their manifestation in posterity differing on the studied signs of forms, i.e. the hybridological analysis is.

History G. also begins with establishment by G. Mendel in 1865 of quantitative patterns of inheritance of characters (see Mendel laws) actually and. In G.'s development and. were of great importance establishment of the linked inheritance of characters by Beytson and Pannet (W. Bateson, R. Page of Punnet) both localizations of genes and creation of genetic maps of chromosomes by T. Morgan with sotr., development of mathematical bases of the theory of G. and. Haldane (J. Century of S. Haldane), R. Fisher and A.S. Serebrovsky. In recent years arsenal of methods G. and. was replenished with the high-allowing receptions recombinational and complementation analysis (see. Recombination analysis, the Mutational analysis), allowing to investigate fine structure of genes. And. depending on research problems it can be carried out at molecular, cellular, ontogenetic and population level.

And. at molecular level became possible, first, thanks to inclusion in number of objects G. and. microorganisms with their special types of recombinational processes and, secondly, thanks to what modern biochemical, methods allow to study in detail not only qualitative and quantitative composition, but also the sequence of monomers in proteins and nucleinic to-takh.

And. at the cellular level it is carried out in that case when the corresponding ancestral features are shown in separate cells. Tetrad analysis at the higher plants, mushrooms and seaweed when products of distribution of homologous chromosomes in meiosis of separate meyotsit (pollen or disputes) can be identified as by origin from the general meyotsit, and on accompanying morfol can be a typical example., to biochemical, or other signs. Also the cytogenetic analysis is important, at Krom the studied ancestral feature is the structure chromosomes (see). Its opportunities sharply increased in connection with opening of methods of differential coloring of the chromosomes on length allowing to identify not only each of couples of chromosomes, but also their certain sites (see. Chromosome map ). Conditionality of many hereditary diseases of the person disturbance not of genes, but their numbers and an arrangement in chromosomes shows relevance of development of the cytogenetic analysis. And. at the cellular level it can be carried out also in cultures of somatic cells for which methods of effective hybridization are developed without what the analysis of patterns of transfer of cellular signs to daughter cells is impossible. In genetics of the person hybridization of somatic cells in culture shall become valuable reception in the analysis of inheritance of characters, first of all biochemical and immunological (see the Geneticist of somatic cells),

G. and. at the ontogenetic (organismal) level it is based on the experiences allowing to learn about genes and their functioning in cells on makromorfo l. to signs of metazoans and vegetable organisms. In this case, unlike G. and. at molecular and cellular level, a subject of observations are not immediate products of functioning of genes in cells, and final phenotypes, i.e. result of complex interaction of all genotype with set of factors internal and the environment. Nevertheless practically G. and. at organismic level has the greatest value.

And. at the population level it is based that the replicated genes depending on dominance or recession, participations in a recombination, and also unequal adaptive value of different alleles (see) are widespread in populations with different frequencies which ratio can be investigated both theoretically, and actually. Comparison of empirical gene frequencies with expected on the basis of different modes of inheritance allows to make the reasonable choice between different theoretical opportunities. To G. and. at the population level it is necessary to address especially often in researches on genetics of the person and the medical geneticist in connection with impossibility of carrying out systematic crossings.

Methods G. and. at all levels, from molecular to population, are complementary, and only their complex allows to capture in general both a structure, and functioning genotype (see).

The genotype of the higher organisms consists, as a rule, of two haploid sets of chromosomes — a maternal and fatherly origin. In turn each of chromosomes genome (see) consists of the sequences of genetic loci which can be busy with different alleles. Depending on what of the parties of the organization of a genotype is studied distinguish the following methods G. and.: genomic, chromosomal, mutational (gene) and analysis of fine structure of a gene.

The purpose of the genomic analysis — to establish of what number of genomes the genotype is made and whether each of genomes on chromosome number «is complete». At the higher organisms perhaps both a deviation of number of genomes from two, and loss or, on the contrary, existence in excess number of separate chromosomes. The majority of the known numerical mutations of chromosomes at the person is the cornerstone of severe forms of hereditary pathology (Turner's syndromes, Klaynfeltera, a Down syndrome, spontaneous abortions, etc.), as defines relevance of the genomic analysis in medical genetics.

The purpose of the chromosomal analysis — identification structural (inside - and interchromosomal) reorganizations without change of chromosome number or a mutirovaniye of the genes which are their part. Restructurings of chromosomes can interfere with normal cellular division, especially maturation division; besides, separate reorganizations can possess independent, sometimes patol, manifestation (see. Chromosomal diseases).

The purpose mutational, or gene, the analysis — studying of possible allelic conditions of genes, and also patterns of their transitions from one state to another as is spontaneous, and under the influence of various environmental mutagen factors (see the Mutagenesis). Studying of intragenic interallelic interactions allowed to reveal a complex structure of genetic loci of the higher organisms and to show that «classical» genes — structures of higher order, than those nucleotide sequences, to the Crimea we will directly apply the principle «one gene — one polypeptide chain» (see. Biochemical genetics).

Except the genotype presented by chromosomes of cellular kernels, as carriers of hereditary information from a cell to a cell also some extranuclear (cytoplasmatic) structures differing in sufficient stability and capable to reduplication and transkriptsionny function can serve. Not chromosomal, cytoplasmic inheritance (e.g., mitochondrial heredity at different organisms, plastid heredity at plants, etc.) makes only a small part in mechanisms of heredity, is intended for performance of highly specialized functions and, at last, is not quite autonomous — partially is under control of nuclear genes (see cytoplasmic inheritance).

Thus, G. and. extends to all levels of the organization of living matter, and also to its hereditary basis — a genotype. And. is the main content of researches in any industry of genetics, including genetics of the person and medical genetics. Without G. and. the solution of such important problems of medical genetics as heterogeneity of hereditary diseases, hereditary polymorphism, early diagnosis of hereditary diseases, their rational prevention, assessment of risk (a possibility of emergence in a family of the patient) and, at last, pathogenetic therapy is impossible.

In process of improvement of methods G. and. open an opportunity and «synthesis» of new genotypes or their elements.

In the long term the methods of genetic synthesis based on detailed quantitative and qualitative analysis of a genotype can become property of medicine at treatment of hereditary diseases of the person (see. Genetic engineering , Gene therapy ).

Bibliography: Dubinin N. P. General genetics, M., 1976, bibliogr.; Lobash e in M. E. The principles of the genetic analysis, in book: Aktualn, vopr. sovr, geneticists, under the editorship of S. I. Alikhanyan, page 7, M., 1966; Serebrovsky A. S. Genetic analysis, M., 1970, bibliogr.

N. P. Bochkov, V. I. Ivanov.