From Big Medical Encyclopedia

FLOOR — set of signs, on the Crimea is made the specific division of individuals or cells based on their morphological and physiological features and allowing to carry out in the course of a syngenesis a combination in descendants of hereditary inclinations of parents. Distinguish a floor men's and women's though, as well as any polarity, it is possible to designate them the signs «+» and «—». However the signs «+» and «—» designate P. only at microorganisms, at animals of a female individual it is accepted to designate the sign «?» (a sign of Venus), men's — the sign «?» (a sign of Mars).

Thanks to a syngenesis in the nature there is that genetic variety of organisms (see. Variability ), a cut serves as material for natural selection (see) and evolutions of types (see. Look ). The syngenesis provides immortality live since somatic cells cannot exist vaguely long even in the optimal conditions created for them in the corresponding experiments. The importance of sexual process is confirmed by the fact that it is found in these or those modifications practically at all steps of evolution of the live world. At the person and the highest animals the sexual differentiation reached such development that existence of bisexual beings is considered as pathology (see. Hermaphroditism ).

As the sexual differentiation occurs in ontogenesis, its predetermination is possible till the moment fertilisations (see) — progamic, during fertilization — syngamic or in the course of the subsequent development — epigamic. The first takes place at rotifers (Rotatoria), a plant louse (Phylloxera vastatrix) and primary kolchets (Dinophilus), the second — at fishes, birds and mammals, the third — at a sea worm (Bonellia viridis). Morphological and fiziol, signs, on the Crimea differ individuals of different floors, call sexual. The signs connected with formation and functioning of sex cells are called primary sexual characteristics. These are gonads (ovaries or seed plants), their output channels, exclaves of the sexual device, copulative bodies. All other signs, on the Crimea one floor differs from another, received the name of secondary sexual characteristics (character of indumentum, existence and development of mammary glands, skeleton structure, type of development of hypodermic cellulose etc.). The differentiation of sex cells occurs in process ontogenesis (see). The period of a sexual differentiation and time of its approach at different types are various. So, dipterous insects already in cytoplasm of an ovum have rudiments which take further active part in process of a differentiation of sex cells. At the person of a cell of a rudiment of gonads for the first time appear in the field of a vitelline entoderm, and then migrate to the area of a coelomic mesoderm where there is laying of gonads. Oogenesis (see) and spermatogenesis (see) significantly differ among themselves since the ovum shall contain a bigger reserve of the substances necessary for bystry development of a germ. The spermatozoon bears densely packed haploid set of chromosomes and, as a rule, represents the cell which almost lost cytoplasm, it easily moves thanks to existence of a flagellum.

At the higher organisms sexual process is carried out by means of sex cells (see. Gametes ). However at somatic cells the possibility of parasexual process, going both in the vitro, and in vivo was established that demonstrates that sexual and somatic cells are a product of a differentiation of the common cellular precursors.

For the correct understanding of biology of P. it must be kept in mind that all living beings, including and the person, are bisexual. This bisexuality can be revealed at any level of a research. In each specific organism there are both female, and male sexual inclinations, their interaction and a ratio bring in process of ontogenesis to preferential formation of signs of this or that floor. Therefore each representative of a certain P. has some signs of an opposite sex expressed to a lesser extent. Sometimes under the influence of a number of internal or external factors there can be a natural or artificial reversion of a floor what classical experiments of M. M. Zavadovsky on change of generative organs testify to.

Bisexuality of individuals is shown already in a stage of embryonic development. The rudiment of a generative organ consists of cortical and brain layers. Preferential development of a bast layer leads to formation of ovaries, and brain — to formation of seed plants. From the moment of emergence of gonads in further sexual development the important role belongs to sex hormones (see). Bisexuality exists also at the hormonal level since, except hormones, specific to this floor, the corresponding glands produce a nek-swarm amount of the hormones inherent to an opposite sex.

It is necessary to distinguish strictly processes of definition of P. (sexual determination) and processes of a sexual differentiation during ontogenesis. Already that circumstance that at the birth the ratio of representatives of opposite sexes is equal about 1:1 allowed geneticists to assume and then and to experimentally confirm that various P.' representatives differ from each other on sets of chromosomes in such a way that one of floors appears gomozigoten (gomogameten), and another — geterozigoten (geterogameten) on one of couples of chromosomes (see. Karyotype ). This couple unlike other chromosomes of set called autosomes received the name of gonosomes; for them repeatedly offered other names — «gonosoma», «heterochromosomes», «allosomes», but any of them did not gain distribution. The gonosomes which are available for female (homogametic) P.'s individuals designate a letter X (X-chromosome), and the gonosomes which are available for male (geterogametny) P.'s individuals designate a letter Y (Y-chromosome). The person has female individuals of a gomozigotna on X-chromosome, and male individuals of a geterozigotna, a set of their gonosomes is presented by chromosomes of X and Y. For types, at to-rykh hetero-gametnym the female is (birds, butterflies), suggested X-chromosome to designate Z, and Y-hromosomu — a letter W. But such double symbolics in scientific literature did not take root. Here is how sets of gonosomes at the person and nek-ry animals look (see the table).


In time meiosis (see), providing formation of haploid sex cells, there is a discrepancy of gonosomes on one in each sex cell. Therefore all ova of the woman bear one X-chromosome (homogametic sex) while one half of spermatozoa of the man bears X-chromosome, and another — a Y-chromosome (heterogametic sex). Fertilization of an ovum the spermatozoon bearing X-chromosome leads to emergence of a female zygote (XX), and fertilization by its spermatozoon bearing a Y-chromosome — to emergence of a men's zygote (XY).

In cases of disturbances of discrepancy of gonosomes during meiosis children with an unusual set of gonosomes are born that is the reason so-called. chromosomal diseases (see). E.g., a set of gonosomes of XXY causes Klaynfelter's syndrome (see. Klaynfeltera syndrome ); the XXXY set — option of a syndrome of Klaynfelter; the XXXXY set — nek-ry mental retardation at children, the expressed sexual underdevelopment, is characteristic a radioulnar synostosis; set XXX — nek-ry mental retardation at children, sometimes is noted by disorders of functions of ovaries; set XXXX and ХХХХХ — clearly the expressed mental backwardness; mosaics of gonosomes of XXY/XY and XXY/XX cause states, similar to Klaynfelter's syndrome (make 5 — 25% of total number of persons with Klaynfelter's syndrome); mosaics of XXX/XX — the state similar to anomaly of XXX; the HO set causes Shereshevsky's syndrome — Turner [sy. ^Тернера syndrome); mosaics of XO/XX and XO/X of XX — symptomatology of a syndrome of Shereshevsky — Turner with various degree of manifestation; the XYY set — the increased growth, sometimes disturbances of behavioural reactions; the XXYY set — the increased growth, lines of a syndrome of Klaynfelter.

At the person, as well as at some other mammals, existence or lack of a Y-chromosome is conducting in a sexual differentiation. The persons bearing a Y-chromosome, as a rule, develop as the man. Such feature of a sexual differentiation allows to assign genetic gender of the person on the basis of the analysis of set of its gonosomes. As an express diagnostic method of a genetic floor use a method of definition sex chromatin (see). Definition of a genetic floor practices in forensic and sports medicine, and also for carrying out the differential diagnosis at a number of the diseases caused by anomalies of gonosomes.

The convincing evidence of participation in a sexual differentiation not only the whole gonosomes, but also the single genes capable to cause reversion of a gender of mammals is obtained. So, there are descriptions of the HH-male. Among theories of gene sex determination the greatest attention is drawn by the theory assuming expressivity of a gene (see), controlling H-Y-antigen of a cellular surface in men's cells. Such assumption is spoken well by almost universal occurrence of this evolutionarily kept antigen at males of mammals and at a heterogametic sex of other animals. It is established that in many cases expressivity of a gene of H-Y-antigen is decisive for male determination. It is found and in the HH-male.

The signs of an organism caused by the genes located in gonosomes are called the signs linked to a floor. The known signs which are the most linked to X-chromosome are hemophilia (see) and color-blindness (see. Color sight ). However in the course of the researches at the person describe all new signs linked to X-chromosome. So, 279 such signs are given in the report of ancestral features made V. Mack-Kjyuziky in 1978. Many of them are precisely mapped. It is accepted to call the signs caused by the genes located in a Y-chromosome golandrichesky since they are given only in the male line. There is a number of the signs controlled by the genes located in autosomes however the certain environment created by the genes causing sexual development is necessary for manifestation of these signs. It is accepted to call such signs the signs caused or controlled by a floor. So, emergence of a bald head — an autosomal dominant character, but is shown it practically only at men (the sign limited to a floor).

Statistically reliable data demonstrate that the ratio of floors at fruits of the person is equal to 1:1. Approximately same it remains also at the birth (sometimes about a nek-eye dominance of boys). But in the subsequent owing to a smaller biol, resistance of males to adverse environmental factors this ratio changes, and the relative number of women increases.

Bibliography: Astaurov B. L. Genetics of sex, in book: Aktualn, vopr. sovr, geneticists, under the editorship of S. I. Alikhanyan, page 65, M., 1966; Bochkov N. P. and Kostrova A. A. A ratio of gender of the person in the embryonal period and among newborns, Dokl. Academy of Sciences of the USSR, t. 200, No. 4, page 973, 1971, bibliogr.; Goldshmidt R. Mekhanizm and physiology of sex determination, the lane with it., M. — L., 1923; Zavadovsky M. M. Floor and development of its signs, M., 1922; Knorre A. G. A short sketch of embryology of the person with elements of comparative, experimental and pathological embryology, L., 1967; Goldschmidt R. Century of Theoretische Genetik, V., 1961; Vogel F. a. M o t u 1 s k at A. G. Human genetics, B. and. lake, 1979.

Of G. Poroshenko.