GENOCOPY

From Big Medical Encyclopedia

GENOCOPY (Greek genos sort, origin + lat. copia a set) — similar changes of one and - the same sign under the influence of different nonallelic genes which sometimes call mimetichesky genes of heterogeneous group. The term «genocopy» is offered in 1957 it. geneticist H. Nachtsheim. Are known at plants and animals, and also at the person. As G. only similarity in final is considered (morfol., fiziol., clinical) signs while primary biochemical, the changes caused by the controlling nonallelic genes are always various.

At the person and animals hereditary disproportionate dwarfism (chondrodystrophia) is known, at a cut a number of externally similar disturbances of a skeleton is controlled by genes of different loci. The pigmental degeneration of a retina at the person, edges is shown by a hemeralopia (a night blindness), progressive concentric narrowing of a field of vision, decrease in sharpness of the central sight and lack of the electroretinogram, can be controlled by several autosomal recessive genes, an autosomal dominant gene and two different recessive genes localized in X-chromosome.

With various mode of inheritance (autosomal and dominant, autosomal and recessive and linked to a floor) are known also for ophthalmoplegias (see), microphthalmias, surdomutisms (see), inborn and infantile cataracts (see). The birth of children with normal sight in marriages between two sick individuals with a recessive inborn amaurosis indicates genetic heterogeneity of this disease. At the person 12 forms of hereditary deafness are known, 6 of which are controlled by autosomal dominant genes, 3 — recessive genes and 3 — the genes localized in X-chromosome.

Hereditarily and biochemical heterogeneous, but clinically similar G. there were number of forms glycogenoses (see), mukopolisakharidoz (see) and sudanophil leukodystrophy (see).

Until recently the weak-mindedness which was considered as uniform nosological unit can be caused by about 70 different hereditary defects of exchange. In view of participation of many genes in formation and functioning of a brain, it is possible to believe that clinically similar cases of weak-mindedness can be caused by mutations not less than one hundred different gene loci.

G.'s emergence is connected with the fact that development of any body represents a difficult chain of the consecutive processes controlled by a large number of genes, and the mutation of each of them can break development and lead to similar final effects. So, three genetically different like a microphthalmia at a mouse significantly differ and pathogenetic. The microphthalmia at mice, homozygous on a gene of fi, is caused by suppression of growth of an eye rudiment owing to what there is no normal inductive impact of an eye bubble on an ectoderm and the otshnurovaniye from it a lenticular bubble is broken. Insufficient growth of a retina is a cause of infringement of development of an eye in mice of a genotype of or/or. Primary disturbance of development of an eye in mice of a genotype of mi/mi is caused by the strengthened growth of an outside leaf of an eye bowl. Anomalies of eyes are shown is similar at animal these three mutant lines: mice with a microphthalmia are blind as a result of an underdevelopment of a retina, existence of cataracts, opacification of a cornea or strong deformation of an eye. Only gistoembriol. the analysis of causes of infringement of development of an eye shows cardinal difference in a pathogeny of these three types of a microphthalmia. Genes initially act on molecular level, controlling synthesis of a certain protein. In this respect action of all genes is specific and distinction of their effects is undoubted. Final effects of genes can be shown phenotypical at various levels: biochemical (e.g., agammaglobulinemia, alkaptonuria, etc.)? physiological (e.g., daltonism, hypertension, etc.) and morphological (anomalies of a structure outside and internals). Final signs are caused, as a rule, by interaction of many genes therefore genes of various loci, blocking development of the same sign in different links, can cause effects, similar on external manifestation.

: the surdomutism in families And yes B is controlled by different alleles of the same gene, and in a family In — other gene; the surdomutism in families And yes B is similar to a surdomutism in a family In, i.e. is a genocopy; at marriage of deaf-and-dumb family members And with deaf-and-dumb members of the family of B all children will be deaf-mutes because in both families the same gene is struck; at marriage of deaf-and-dumb family members In with deaf-and-dumb family members And yes B or their descendants healthy children because in families And (B) and In a surdomutism it is caused by different genes (symbols — see St appear. Genealogical method , fig. 1).

Establishment biochemical, the defects which are the cornerstone of hereditary diseases or primary earliest deviations in a morphogenesis of internal and outside bodies is approach to an exact differentiation of hereditary anomalies. A decisive argument for G.'s distinguishing as independent nosological units are results genetic analysis (see). The most obvious case of a genokopirovaniye is various mode of inheritance of a similar disease in different families. However if similar anomalies have an identical mode of inheritance in different families, then to resolve an issue, same or different genes they are controlled, much more difficult. In case of the diseases controlled by the recessive genes localized in X-chromosome (e.g., hemophilia), the issue of G.'s exception can be resolved if in marriage from the sick man and the woman from the family burdened same getting sick the sick girl is born.

It is slightly simpler than identification of G. caused by autosomal recessive genes in comparison with a case of the inheritance linked to a floor. The birth in marriage at the individuals (fig., II, 8 and 9) having the similar disease controlled by autosomal recessive genes, the child struck with the same anomaly or several children of any floor (fig., III, 9 — 12) undoubtedly demonstrates that this anomaly is controlled by the same mutant gene or, as a last resort, different alleles of one locus (see Alleles). All children from such marriage will have a disease, similar to parents. From marriage of individuals with clinically identical surdomutism controlled by different autosomal genes (fig., III, 7 and 9), clinically healthy children will be born (fig., IV, 1 — 6).

The genetic analysis is complicated by a malodetnost of the majority of families and that circumstance that ancestral features along with various degree of manifestation (various expressivity) can be shown not at all individuals (see. Gene ).

Existence in human populations of G. needs to be considered both in researches on medical genetics, and in medical practice. E.g., most of authors gives the microphthalmias sported about frequency of a gene, without specifying what forms of a microphthalmia are investigated. The same can be told about an achondroplasia and some other anomalies. It is undoubted what in many works combined several G. controlled by different genes as a result of it data on a mutation rate of genes were overestimated. More exact sported about frequency of genes are received for the diseases connected with insufficiency of certain enzymes, in particular akatalaziya (see), galactosemia (see), fenilketonuriya (see), etc., and also clinically and pathogenetic well studied diseases of blood. The further genetic analysis and detailed studying of a pathogeny will undoubtedly promote more exact differentiation of hereditary diseases that is an indispensable condition for development of effective methods of therapy and prevention.


Bibliography: B. V. grooms. Biological modeling of hereditary diseases of the person, M., 1969, bibliogr.; Problems of medical genetics, under the editorship of, V. P. Efroimsona, M. — Warsaw, 1970; Stern K. Fundamentals of genetics of the person, the lane with English, M., 1965; McKusick V. A. Heritable disorders of connective tissue, St Louis, 1972; Nachtshe im H. Mutation und Phanokopie bei Saugetier und Mensch, Experientia (Basel), Bd 13, S. 57 # 1957.

B. V. Konyukhov.

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