From Big Medical Encyclopedia

CODOMINANCE — the phenomenon characteristic of all higher organisms consisting in joint manifestation of both alleles at a heterozygote.

Value of the phenomenon To. in biology and medicine first of all it is connected with a possibility of studying biochemical, and immunol, methods of manifestation of both alleles (see) in ontogenetic, population or evolutionary aspects. The codominant nature of action of allelic genes allows to establish the beginning of activity, the place and duration of action of each allele in ontogenesis, and also the frequency of genes in human populations and different types of live organisms. It is of great importance for the solution of questions of change of fabrics and bodies, and also identifications of heterozygous carriers of hereditary anomalies that is a necessary condition for carrying out medicogenetic consultation.

The phenomenon To. it was for the first time revealed immunol, methods. An example To. inheritance of antigens of blood groups of AB and MN at the person is (see. Blood groups ). Synthesis of AV antigens is controlled by different alleles of one locus which is designated by an I symbol. Codominant manifestation of alleles of I And and I In in a heterozygote of I A I B leads to the fact that individuals of the IV blood group in erythrocytes at the same time have antigens A and B. Therefore, synthesis of AV antigens is controlled by allelic genes which manifestation kodominantno. Synthesis of MN antigens is also controlled by codominant alleles therefore at erythrocytes of heterozygous individuals there are at the same time antigens M and N.

Determination of each antigen a codominant gene (i.e. antigen is present irrespective of whether there is a gene in gomo-or a heterozygous state) is one of philosophy immunogenetics (see). Codominant action of genes seldom occurs at heterozygotes for morfol, signs, but is characteristic of manifestation of gene effects at the level of proteinaceous molecules.

The codominant mode of inheritance is characteristic of enzymes and serum proteins, in particular of gaptoglobin and transferrins. The codominant nature of manifestation of effects of genes at the proteinaceous level defines polymorphism of proteins or existence of their genetic options. So, along with eurysynusic polymorphism of blood groups in populations of people the hereditary polymorphism of gaptoglobin caused by two codominant allelic genes of Hp1 and Hp2 and also the polymorphism of transferrins caused by a series of codominant allelic genes is found

. With the phenomenon To. emergence in heterozygotes of hybrid proteinaceous molecules which consist of the polypeptide chains differing on structure coded by two alleles of one gene locus is connected. Hybrid proteins are present only at heterozygotes and cannot be formed at homozygous individuals.

It is possible to find several molecular forms of the enzymes called by isoenzymes. It is connected, in particular, with existence of multiple alleles. A multiple allelism and the phenomenon To. determine distinctions between certain members of population by a set of isoenzymes and other proteins.

See also Dominance , Mendel laws , Mutational analysis .

Bibliography: Dubinin N. P. General genetics, M., 1976; Makkyyusik V. A. Ancestral features of the person, the lane with English, M., 1976; Problems of medical genetics, under the editorship of V. P. Efroimson, etc., page 172, M., 1970; Harris G. Fundamentals of biochemical genetics of the person, the lane with English, M., 1973; Efroimson V. P. Immunogenetics, M., 1971,

B. V. Konyukhov.