From Big Medical Encyclopedia

HEREDITY — property inherent in all organisms to provide in a lineage succession of identical signs of l of features of development — the morphological, physiological and biochemical organization of living beings, character of their ontogeny (ontogenesis). N.'s phenomenon is the cornerstone of reproduction of life forms on generations that radically distinguishes live from lifeless.

Knowledge of laws H. allows to understand mechanisms of transfer of hereditary information from parents to children, pattern of formation hereditarily of the caused signs and a role of genes in complex processes of life activity of an organism. The N of mankind with its incalculable quantity of various genes provides an infinite variety of identity. Development of evidence-based methods of reduction of a genetic load of hereditary anomalies will promote preservation of hereditary human nature.

Diagrammatic representation of monogenic (oligogenic) inheritance of characters: at the left — inheritance dark (dominant character) and light (recessive character) coloring at fishes; on the right — inheritance of an ostistost (dominant character) and baldness (recessive character) at wheat; in all cases in firstgeneration all individuals are carriers of a dominant character, and in second generation (on average) on three individuals with a dominant character one individual with a recessive character appears.

Distinguish chromosomal and extra chromosomal N. Hromosomnaya N., connected with distribution of carriers of heredity (genes) in chromosomes, is based on the principles which for the first time are accurately formulated in G. Mendel's works, and then repeatedly opened by Korrens (K.Correns), E. Tschermak and X. de Fris. N.'s role in transfer of signs to posterity is especially accurately shown at inheritance of Mendelian characters, i.e. such ancestral features, to-rye in posterity are split on monogenic type inheritance (see) according to Mendel's (fig.) laws.

Extra chromosomal, or cytoplasmatic, N. (see. cytoplasmic inheritance ) it is shown in inheritance of characters, to-rye are controlled by the extra chromosomal, cytoplasma hereditary factors localized at animal organisms in mitochondrions (see), at plants — in mitochondrions and plastids, at bacteria — in plasmids (see). The cytoplasmatic elements having property of transfer of hereditary information are distributed between daughter cells accidentally therefore accurate Mendelian splitting in these cases is not observed. All systems of extra chromosomal N. interact with chromosomal genes or their products.

Profound studying of N. began only in 19 century, and significant progress in this area was made only in 20 century. After opening of fundamental laws of N. by G. Mendel became undoubted that N. is defined by material factors, in the subsequent the called genes (see. Gene ). However in 1750 Mopertyui (R. of L. M of Maupertuis) and in 1814 J. Adams described nek-ry features of inheritance of separate signs at the person. In 1875 Mr. F. Galton offered twin method (see) for differentiation of a role of N. and Wednesday in development of signs in the person. He proved a genealogical method of the analysis not only discrete, but also continuous signs at the person (see. Genealogical method ) also developed a number of statistical methods, from to-rykh the method of calculation of a correlation coefficient is especially valuable.

In formation of the doctrine about N. creation by T. Morgan and his school was of great importance chromosomal theory of heredity (see) when it was established that the gene represents material structure in chromosomes of a kernel of a cell. During the period from 1900 to 1930 the materialistic foundation for the modern doctrine about N is laid.

In the late twenties — the beginning of the 50th of 20 century the drobpmost of a gene was shown, the phenomenon of a position effect of a gene, communication of genetic elements with DNA are established and some other important opening is made. During this period the chromosomal theory of N. is exempted from earlier mechanistic and idealistic mistakes inherent to it, in particular from the theory of an autogenesis.

After opening in 1953 structural and funkts, the nature of molecules DNA as carriers of genetic information the present stage of studying of problem N began. The most important achievement of this stage is establishment of generality of hma-terialny bases of N. on the basis of molecules DNA and RNA thanks to what the principle of general communication in the organic world triumphed.

As the main complete unit of life serves the cell having a kernel and cytoplasm and to a kernel, but not cytoplasm possesses the main role in ensuring succession of signs and features of development. E.g., the men's sex cell of the person contains very few cytoplasm, is 85 000 times less, than an ovum (a female sex cell), however a contribution of both sex cells to heritage of future child is approximately identical. The kernel supports threadlike structures — chromosomes (see), the representing educations consisting of DNA and protein.

The main form of reproduction of organisms — sexual process when the separate individual arises from an oospore, a pla of a zygote. Self-reproduction of organisms, generally plants, can be carried out with the help vegetative reproduction (see). In this case descendants arise from parts of a parent individual. At a syngenesis there is filial segregation of posterity depending on genotypes owing to what, e.g., during the crossing of hybrid or high-heterozygous plants return to wild forms and loss of valuable high-quality signs is often observed. At vegetative reproduction the long time is possible to keep genetic properties of grades. It is established that any plant cell which did not lose during the differentiation of a kernel and cytoplasm can turn in culture in kallus-ny, or zigotopodobny, a cell to publish the beginning to a new organism. From one differentiated cell the whole plants of carrots, tobacco, a parsnip, etc. were received.

The hereditary information concluded in genes of each individual is a result of historical development of this look and a material basis of future evolution. N.'s phenomenon is considered in the form of the complex molecular intracellular system providing storage and implementation of information now, according to a cut life of a cell, development of an individual and her life activity are carried out. Implementation of the hereditary information which is written down by alternation of nucleotides in DNA of a zygote (see. Genetic code ), results from continuous interferences of a kernel and cytoplasm, intercellular interactions and hormonal regulation of activity of genes.

In process genotype (see) constantly interacts with Wednesday. Nek-ry ancestral features, napr, color of eyes or a blood group, do not depend on conditions of the environment. At the same time environmental factors exert on development of the quantitative characters, such as growth and body weight caused by polygenic system, a great influence. Manifestation of effects of the genes causing, e.g., obesity in many respects depends on food therefore by means of the corresponding diet it is possible to fight to some extent with hereditarily the caused completeness.

Material carriers H. contain information not only for development normal, but also patol, signs. So, different mutations (see) — the genetic load accumulated in a gene pool of the person are an origin of a large number of hereditary anomalies, from to-rykh hundreds of millions people of our planet suffer. More than 2000 nosological units of hereditary diseases of the person are known (see. Hereditary diseases ). Diseases with a dominant mode of inheritance or linked to a floor are found rather easily. It is more difficult to establish value H. in development of such eurysynusic polygenic diseases with hereditary predisposition as an idiopathic hypertensia, atherosclerosis, a peptic ulcer, schizophrenia, bronchial asthma, etc. Frequency of emergence and weight of a course of these diseases depend on a specific combination of environmental factors and hereditary predisposition. Such malformation as, e.g., the split sky, is result of interaction of many genes with various teratogens in the period of an embryogenesis when there is an accretion of lateral palatal ledges.

The mankind is faced by a task to reduce a genetic load of hereditary diseases and to protect the N. from the harmful action of radiation and chemical connections which is steadily increasing in process of scientific and technical progress.

See also Genetics , Variability , Medical genetics .

Bibliography: Berdyshev K. D. and Krivoruchko I. F. Genetics of the person with fundamentals of medical genetics, Kiev, 1979; Bochkov N. P. Genetics of the person, M., 1978; Gershenzons.M. Fundamentals of modern genetics, Kiev, 1979, bibliogr.; Dubinin N. P. General genetics, M., 1976; Watson Dzh. Molecular biology of a gene, the lane with English, M. / 1978; Ms To usi with k V. Mendelian inheritance in man, Baltimore, 1978.

B. V. Konyukhov.