POLYMORPHISM

From Big Medical Encyclopedia

POLYMORPHISM in genetics

POLYMORPHISM in genetics (grech, polymorphos diverse) — the term designating manifestation of individual, discontinuous variability of live organisms. Originally it was widely used for designation of any discontinuous variability in a look (e.g., castes of public insects, age differences in coloring, sexual dimorphism, etc.), however later such distinctions began to call a polifenizm, and the term «polymorphism» according to the definition given by the English geneticist Ford (E. Century of Ford), to designate existence in the same population of two or more well the distinguishable forms capable to appear in posterity of one female and meeting with frequency, rather high to exclude maintenance of the most rare of them repeatedly arising mutations. The concept «polymorphic» should be distinguished also from the concept «polytypic», a cut designates difficult taxonomic categories (e.g., a polytypic look — the look presented by two or more subspecies, etc.).

As discrete signs of an organism are controlled, as a rule, by allelic genes or blocks of closely linked genes, so-called supergenes (see. Gene ), some researchers suggest to mean existence in population of two or more by genetic P. alleles (see) one locus (see), meeting rather often.

The item affects any features of a phenotype at any level, including on cellular and molecular. E.g., P. of erythrocyte antigens at the person (blood group), structure of chromosomes — inversions, duplications, accessory chromosomes is well-known (see. Chromosomal polymorphism ).

In the late sixties — the beginning of the 70th of 20 century thanks to development of sensitive methods, hl. obr. various methods electrophoresis (see), in populations of animals and the person wider P. on the genes responsible for protein synthesis of blood and other fabrics which is inherent in nearly a third of all studied gene loci coding protein synthesis of both the fermental, and not fermental nature (see is found. Isoenzymes ).

Biol, value of such wide hereditary variability of populations and types is up to the end not deciphered, and on this matter there are two points of view. It agrees one of them biochemical P. is supported in populations thanks to selection, i.e. has adaptive value, agrees another — biochemical P. shall be referred to category of selection and neutral variability. Nevertheless there is a set of the established facts testimonial of exclusive value of the phenomenon of genetic P. for biology and medicine. Constant presence at population with rather high frequency of two or more discrete forms — genotypes (see) — means that such P. is supported due to preferential selection of heterozygotes. Polymorphism of hemoglobin, eurysynusic in populations of people of an Asian and African origin and leading to the disease known under the name can be an example of it sickemia (see). Anemia is connected with homozygosity on a gene of s which causes formation of abnormal hemoglobin. Homozygotes of ss perish soon after the birth. However it became known that the high frequency of this gene in populations remains thanks to the fact that heterozygotes of Ss are surprised malaria less, than homozygotes of SS. In the conditions of constant presence in the environment of the causative agent of malaria in populations the steady ratio of all three genotypes — SS, by Ss and ss, the so-called balanced polymorphism is supported.

The similar or similar mechanism is the cornerstone of P.'s maintenance blood groups and various proteins in human populations that along with other proofs is confirmed also by discovery of correlation (associations) between this or that blood group and resistance to certain diseases. E.g., among patients with stomach ulcer and a duodenum the blood group About occurs respectively for 10 and 17% more often than among other part there are populations. Frequency of a blood group And above at patients with nek-ry forms of anemia and a diabetes mellitus is reliable. Also certain role of polymorphism of fabric antigens in stability of a human body to a nek-eye is recently shown to diseases.

Each individual possesses a unique genotype concerning blood groups and proteins, and this uniqueness affects on its physical and fiziol, features, including and resistance to diseases of both the exogenous, and endogenous nature. It is obvious that communication between a polymorphic condition of a gene and its functional role not always has so pronounced specific character as in case of drepanocytic anemia, and is determined by a certain integral structure of a genotype by set of many polymorphic genes controlling nonspecific biol, stability of an organism much more often.

Thus, though not everything in genetic P.'s phenomenon is found finally out, its analysis allows to study genetic processes in populations of different types of animals and the person and to resolve the important issues connected with their origin, evolution and adaptation to the environment. Genetic P. allows to use also blood groups and electrophoretic options of proteins as genetic markers for the solution of a number of problems of forensic medicine (e.g., at identification of genotypes by means of a research of samples of blood and others biol, it is liquid - Tay, at the proof of monozygotes-nosti of twins, at the solution of questions of a doubtful paternity, etc.), for drawing up optimum schemes of organ and tissue transplantation, for detection of bonds between a genotype and resistance to various diseases. It is necessary to specify, however, that genetic «maintenance» of a look does not come down to only one variability and that along with P. it is necessary to consider the phenomenon of a genetic monomorphism when the look in general is presented by only one, prevailing genotype, and the frequency of alternative forms does not exceed probability of a repeated mutirovaniye.

There are instructions on the fact that the monomorphic condition of a gene is defined by its important functional role in an organism in this connection many again arising mutations of the corresponding genes, as a rule, are swept aside by selection at early ontogenetic stages. If carriers of such mutations survive, then they are struck hereditary diseases (see), belonging to the category of so-called inborn disbolism.

POLYMORPHISM in pathology

POLYMORPHISM in pathology (Greek polymorphos diverse) — variety of structural manifestations of pathological process in bodies, fabrics and cells.

In the general pathology of P. it is observed at the compensatory and adaptive processes arising at various stages of a course of a disease. Compensatory processes (see) are very various and usually develop in separate systems, bodies and body tissues. E.g., at an osteanagenesis in a zone of a change the bone callosity can be presented by both fibrous connecting fabric, and osteoarticular structures. Besides, P. is noted at a metaplasia of fabrics (see. Metaplasia ) and in process organizations (see). In private pathology of P. it is shown in variability morfol, pictures of a number of diseases (tuberculosis, a lung fever, etc.) under the influence of the natural and induced factors (see. Pathomorphism ). In particular, the current of a lung fever can begin with a stage of red hepatization or gray hepatization, and in nek-ry cases it has the migrating character. More often the concept «polymorphism» is used for morfol, by characteristics of tumoral growth.

Distinguish fabric, cellular and nuclear P. Tkaneva P., characterized by various ratio of a parenchyma and a stroma, meets, e.g., in conditions hron, inflammations, at Krom owing to dystrophy (see. Dystrophy of cells and fabrics ) and regenerations (see) various cellular elements, the bigger or smaller number of vessels of various caliber come to light. Fabric P., napr, at cirrhosis, it is shown by development of uneven layers of fibrous fabric, among to-rykh accumulations of hepatocytes of various size and a form are located. At microscopic examination of tumors, napr, adenocarcinomas, find ferruterous complexes of various size and a form. So, at a prostate cancer the size of ferruterous complexes varies over a wide range, their form is various, is frequent with scalloped outlines and numerous bukhtoobrazny protrusions. A considerable variety of size and a form tyazh and nests of tumor cells have at planocellular cancer.

Cellular P. is characterized by structural change and functions of cells in this connection they can have various size and the form. Cellular P. can be observed at regeneration as a result of an unequal maturity of cells, at various dystrophies. In malignant new growths tumor cells usually have various size and the form (most often wrong), in cytoplasm find various inclusions (fatty vacuoles, fragments of the destroyed kernels, etc.).

Emergence of kernels of various size and a form, various patol, forms of a karyokinesis is characteristic of nuclear P. So, in tumor cells the kernel can occupy almost all cytoplasm or regarding cases is sharply reduced in sizes. Due to the disturbances mitosis (see) there are huge multinucleate cells. Kernels of nek-ry cells intensively are painted, become hyperchromic. At gidropichesky dystrophy of a kernel of cells are increased in volume, rounded shape, with the rarefied nucleohyaloplasm. Sometimes in kernels signs take place pycnosis (see). In the conditions of regeneration of a kernel can get the wrong outlines, in them redistribution is noted chromatin (see). Often in the conditions of regeneration and pathology P. of intracellular structures, such as is found mitochondrions (see), cytoplasmic reticulum, lysosomes (see).

POLYMORPHISM in chemistry

POLYMORPHISM in chemistry (Greek polymorphous diverse) — ability of the same chemical compound or an element to form depending on external conditions (temperature, pressure, etc.) various crystal forms (modifications). Items explain with ability of the same atoms or molecules to form various crystal lattices differing in the stability. P.'s phenomenon in chemistry is opened by E. Mitscherlich in 1821 P. is observed for simple substances (so-called allotropy), for many organic and inorganic compounds, and also for minerals. Diamond and graphite, white and violet (red) phosphorus, etc. can be examples of allotropic simple substances. Calcite and aragonite — polymorphic modifications of calcium carbonate can be P.'s example of chemical connections. Two main types of P. are known: enantiotropy (reversible transformations) and monotropy (irreversible transformations).

The substances which are in various polymorphic modifications possess different physical. - chemical properties and different biol, activity; e.g., growth of hemophilic bacteria on the synthetic medium replacing blood happens in the presence in the environment of gamma Fe 2 O 3 , and at presence an alpha-Fe 2 O 3 bacteria perish.



Bibliography:

polymorphism in genetics

Altukhov Yu. P. and Rychkov Yu. G. Genetic monomorphism of types and its possible biological value, Zhurn. general biol., t. 33, No. 3, page 281, 1972; Bochkov N. P. Genetics of the person, M., 1978; Mayr E. Populations, types and evolution, the lane with English, M., 1974; Harris G. Fundamentals of biochemical genetics of the person, the lane with English, M., 1973; Ehrlich P. and Holm R. Process of evolution, the lane with English, M., 1966; With a v and 1 1 i - S f about of z a L. L. a. Bod-sh e of W. F. The genetics of human populations, San Francisco, 1971; Ford E. B. Polymorphism and taxonomy, in book: The new systematics, ed. by J. Huxley, p. 493, L., 1941.

polymorphism in pathology

Davydovsky I. V. General pathology of the person, page 506, M., 1969; With t r at to about in A. I. and Serov V. V. Pathological anatomy of page 159, M., 1979.

polymorphism in chemistry

Nekrasov B. V. Textbook of the general chemistry, page 382, M., 1981; Not - N and c of e with to at To. The general chemistry, the lane from Romanians., page 130, M., 1968.


Yu. P. Altukhov (polymorphism in genetics), G. M. Mogilevsky (polymorphism in pathology),

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