GENOTYPE

From Big Medical Encyclopedia

GENOTYPE (Greek genos sort, origin + typos form, sample; synonym: idiotype, genetic constitution) — set of the genes localized in chromosomes and in autoreprodutsiruyushchikhsya (self-replicating) cytoplasmatic structures of a zygote. A phenotype — set of signs and properties of an organism which manifestation is caused by its G.'s interaction with conditions internal and the environment. The terms «genotype» and «phenotype» are offered dates. the biologist W. Johannsen in 1909 — not just the sum of genes, and the high-organized system of the interacting elements which is characterized by such factors as participation of many genes in definition of one sign (polygenic determination of signs), participation of one gene in definition of several signs (see. Pleiotropia ), heterozygosity (see. Mendel laws ), features of domination (see. Dominance ) and gene interactions. The nature of phenotypical manifestation of genes in many respects depends also on their Interposition in System.

During the moving of genes to unusual situation in result of chromosomal reorganizations the change of their manifestation most of which often is expressed in weakening of domination (position effect) is observed. The concept «genotype» is used sometimes for designation of distinction between individuals on one or several couples of allelic genes (see. Alleles ). E.g., patients with hemophilia have mutant G. in comparison with normal G. of healthy people.

It is more correct to consider as set only of those genes which have phenotypical manifestation, i.e. can be found with the help genetic analysis (see).

Implementation of hereditary information represents complex multi-stage process and includes not only interaction between separate elements of genetic system, but also not chromosomal influences, coming from zygotes of maternal cytoplasm, the maternal environment, egg and an embryo, the factors brought in a zygote from the outside and between all other internal and external factors which can influence during life of an individual phenotypical manifestations of ancestral features develops in a cut. The direct connection between G. and a phenotype can be only in rare instances established: individual distinctions on blood groups as they are caused only by G.'s structure since the genes defining blood groups have always the same manifestation can be an example of it.

If the phenotype of any somatic cell entirely depends only on G., then it call autonomous. However, as a rule, the phenotype of fabric cells is defined by both their G., and influence of the environment, in particular the diffusing products of other cells. The phenotype of fabric or body is caused by even more complex cellular and interfabric relationship and is controlled by regulatory systems of an organism. In a phenotype all genotypic opportunities are never implemented, and it is only a special case of implementation of G. in specific conditions. Therefore even between the enzygotic twins having completely identical G. it is possible to reveal noticeable phenotypical distinctions if they developed in different conditions. Gena (see. Gene ) only define the direction of development of this or that sign, providing the specific range of its variability depending on conditions of the environment (reaction norm). E.g., the number of erythrocytes at an individual is caused genetically. At the same time their number will depend also to a large extent and on fluctuations of partial pressure of oxygen in free air. However fluctuations of number of erythrocytes are possible only within the reaction norm determined by G.

Specific and nonspecific external influences can modify sometimes so development of an organism that individuals with the signs characteristic of other gene result. Such individuals call phenocopies (the phenotypical changes caused experimentally sometimes call morphosis). The persons having diabetes and receiving insulin are phenocopies of the individuals who do not have diabetes as insulin prevents effects of the corresponding mutant genes. The posterity of such people can have diabetic G. since an insulin therapy makes only phenotypical impact. On the other hand, the injury, surgical intervention, inflammatory processes in a pancreas, an experimental animal of antiinsulin antibodies, hormones of a hypophysis or adrenal gland lead introduction to development of the phenomena of diabetes. Such induced diabetes will not be inherited. Under certain conditions ionizing radiation, many chemical agents, some medicines can be the cause of emergence of phenocopies. So, use of a thalidomide in Germany and England as a hypnagogue in early durations of gestation led to emergence of disturbances in formation of a skeleton of the extremities of a fruit imitating the known hereditary anomalies at the person.

Not heritability of phenocopies is explained by the fact that they are not connected with transformation of hereditary information. A typical example of influence of internal environment in implementation of a mutant gene is development of early weak-mindedness and other secondary symptoms at fenilketonuriya (see). It is established that primary effect of a mutant gene in this case is the inactivation of enzyme of a fenilalaningidroksilaza, it in turn blocks transformation of phenylalanine into tyrosine, leads to accumulation of phenylalanine in blood and finally to development of a disease.

Among the factors of internal environment leading to change of manifestation of genes, are of great importance gender and age of an individual. The fact that the beginning of various hereditary diseases is often connected with a certain age interval demonstrates to it; there is a dependence in manifestation of genes on a floor. E.g., such signs as a labium leporium, gout and baldness, much meet more often at men whereas spina bifida — at women.

The correct understanding of interrelation of G. and a phenotype defines tactics of the doctor concerning the majority of hereditary diseases. In certain cases it is possible to liquidate practically all symptoms of a disease, without influencing directly its reason, i.e. a mutant gene. So, e.g., by means of a special diet with sharply lowered content of phenylalanine it is possible to prevent completely development of weak-mindedness at a fenilketonuriya. Crucial importance for treatment of similar diseases gets definition of time of the beginning of action of mutant genes in ontogenesis. At assessment of danger of some medicinal substances it is necessary to consider not only their mutagen properties, but also influence on phenotypical effects, in particular on emergence of phenocopies.

The role of medical genetics consists in normal G.'s monitoring, in prevention and treatment of hereditary defects, in specific G.'s accounting at the prof. selection.

Set of the signs making a social appearance of the person should be distinguished from his phenotypical features. Social features of the normal person are defined in a decisive way not by its G., but that specific sociohistorical situation, in a cut he lives. Transformation of inner world of the person at the present stage of social development does not demand any radical reorganization it.


Bibliography: Dubinin N. P. General genetics, M., 1976; Mack - Laren A. Nasledstvennost and Wednesday at the cellular level, Ontogenesis, t. 4, No. 3, page 227, 1973; Problems of medical genetics, under the editorship of V. P. Efroimson, etc., M.-— Warsaw, 1970; Stephenson A. and Davy-with about N B. Medicogenetic consultation, the lane with English, M., 1972; Harrison J., etc. Human biology, the lane with English, M., 1968; Sh t of e r N To. Fundamentals of genetics of the person, the lane with English, M., 1965; G u of of d about n J. Century of Nuclear transplantation and the control of gene activity in animal development, Proc. roy. Soc. B, v. 176, p. 303, 1970; L e n z W. Diagnosis in medical genetics, Proc. 3D Int. congr. of human genetics, ed. by J. F. Crow a. J. V. Neel, p. 29, Baltimore, 1967, bibliogr.; Whittinghill M. Human genetics and its foundations, N. Y., 1967.

A. P. Akifyev.

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