From Big Medical Encyclopedia

SEX CHROMATIN — the site of a kernel of the somatic cell which is in interphase, representing the condensed gonosome; as a result of condensation of X-chromosome X-chromatin, and condensation of a Y-chromosome — Y-chromatin is formed. At people with normal structure of chromosomes (see. Karyotype ) somatic cells of women contain X-chromatin, and in somatic cells of men — Y-chromatin. On existence of these educations the genetic sex of the individual can be defined (see. Floor ), that the wedge, forms of a testicular and ovarian dysgenesis finds practical application at diagnosis various (see. Dysgenesis of gonads ), an approximate research of individuals on false — pseudohermaphroditism (see) or true hermaphroditism (see), in court. - medical practice, etc.

X-chromatin (a so-called little body Burra) as specific to a female tsitol, the sign was for the first time described by Barre (M. Barr) and E. G. Bertram in 1949; one of two X-chromosomes in an early embryogenesis is genetically inactivated (geterokhromatinizirutsya) and remains to the life of a somatic cell condensed during all interfazny period. Dekondensation of geterokhromatinizirovanny X-chromosome in a somatic cell does not mean its genetic activation. The second X-chromosome in a female cell and X-chromosome in a men's somatic cell do not form X-chromatin. Y-chromatin forms at the expense of a part of a long shoulder of a Y-chromosome; it consists of the heterochromatin condensed in an interfazny kernel and capable to fluoresce intensively after coloring by quinacrine and others flyuorokhromam (see). The test from flyuorokhroma for definition of a sex of cells on Y-chromatin was for the first time offered by Kaspersson (T. Caspersson) in 1970.

During the definition of a genetic sex of the individual of his cell investigate both on H-, and on Y-chromatin. For this purpose receive cellular material (the most various fabrics can be its source though it is more preferable those, for to-rykh preliminary cultivation of in vitro is not required; for definition of X-chromatin most often use smears from a mucous membrane of a cheek, is more rare than a mucous membrane of a vagina, and also a cell of hair follicles; for prenatal diagnosis of a floor of a fruit use amniotic cells. The maintenance of Y, in addition to the listed fabrics, it is possible to define also in spermatozoa. Fine material for the analysis X-and Y-chromatin are single-layer cultures of cells, usually fibroblasts. In the cultivated lymphocytes of blood Y-chromatin well comes to light. Fixing of drugs is carried out to their dehumidification on air, usually fixed methanol or ethanol mixture and acetic to - you (in the ratio 3:1) or only ethanol. Methods of coloring for identification X-and Y-chromatin are various. X-chromatin comes to light during the coloring of drugs the main not fluorescent dyes better: main fuchsin, thionine, acetoorcein, toluidine blue, etc. Stained preparations dry up and study with oil immersion in a transmitted light. Y-chromatin is revealed during the coloring of drugs of a flyuorokhromama — derivatives acridic orange: quinacrine, quinacrine-yperite, quinacrine-propyl. Drugs are concluded in special buffer solution and studied in an ultraviolet light by means of luminescent microscope (see). The analysis is carried out on the diconnected, spread cells. Cuts of fabrics for P.'s definition x. use only when it is impossible to receive smears or contact preparations of a cut of body.

A little body Barra in a normal diploid cell has the form of a triangle, round or even rhabdoid education, the average linear size to-rogo 1 micron. Very often the little body Burra is on the periphery of a kernel and quite often adjoins to a nuclear envelope. The size, a form, situation in a kernel and dense coloring allow to distinguish X-chromatin from glybok the condensed chromatin of other chromosomes. Frequency, about a cut X-chromatin meets in cells, depends on a condition of an organism (the hormonal status, an exercise stress, etc.) * It is low at newborn girls in the first 2 — 3 days of life. At the puberal woman the frequency of occurrence of X-chromatin fluctuates during the different periods of a menstrual cycle, is various in different fabrics and never reaches 100%. In cells of a mucous membrane of a cheek X-chromatin is found in 25 — 60% of cells, in the fibroblasts cultivated by in vitro — in 40 — 80% of cells, in not cultivated amniotic cells approximately in 5% of cells. In granulocytes X-chromatin has an appearance of a drum stick; low frequency of identification (1,5 — 5%) and difficulty of a differentiation of this education with other nuclear structures limited practical distribution of this test. In polyploid cells the number of little bodies Burra is multiple to number of diploid sets of chromosomes. Cytologic similar to X-chromatin of a glybka of chromatin are found in men approximately in 1% of cells.

The sizes of Y-chromatin in normal diploid cells at different individuals strongly differ that is connected with big fluctuations of length of the Y-chromosome. At diagnosis of a floor on Y-chromatin it is necessary to remember that individuals or meet insignificant amount of heterochromatin in Y-xpo-mosome or at all deprived of heterochromatin, and nondetection of Y-chromatin at such persons is not the fact denying their belonging to a male. At most of men Y-chromatin looks rather large (0,3 — 1 microns), brightly shining formation (little body) of usually rounded shape; in separate cells it can have double structure or to be a little diffusion. On the periphery of a cellular kernel the Y-little body is located less than a little body Burra. At a kernel there are brightly shining glybk of chromatin of other chromosomes which to distinguish from Y-tel-tsa usually easily. Frequency of occurrence of Y-chromatin significantly differs in different fabrics. In cells of a mucous membrane of a cheek it is found in 20 — 80% of cells, in cells of a hair follicle in 70 — 90%, in peripheral blood lymphocytes in 60 — 87% of cells. Fluorescent little bodies, similar to a Y-little body, in cells of the woman (autosomal heterochromatin) meet approximately in 5% of cells. At the women pregnant with a fruit of a male, a cell of the last can get into a blood channel of mother. They are found on availability of Y-chromatin in them. For definition of a genetic floor on Y-chromatin it is recommended to see not less than 50 cells.

Practical application of the test for P. x. doubly. This test is used for sex determination of the individual on his cells, ever the individual is unavailable to a research (prenatal diagnosis of a floor of a fruit, court. - medical examination, etc.) or when a mass inspection of compliance of a phenotypical (passport) floor genetic is carried out (e.g., at inspection of women at sports competitions). Sex determination of a fruit is vnutriutrobno carried out at suspicion on the hereditary disease linked to a floor (hemophilia, some forms of muscular dystrophy, etc.), for the purpose of prevention of the birth of incurably sick child.

At inspection of patients about a wedge. manifestations of disturbance of a sexual differentiation and in other cases when the exact description of a condition of gonosomes, irrespective of results of the analysis on P. is necessary x. resort to the chromosomal analysis (see. Chromosomes ).

P.'s definition is especially frequent x. it is used for preliminary diagnosis of deviations in number or structure of gonosomes when investigated has disturbances of sexual development. Simplicity and speed of performance allow to apply the test for P. x. at mass inspection of newborn and other children for the purpose of detection of anomalies of gonosomes. The final diagnosis is made after studying chromosomal complement (see). Deviations in system of gonosomes towards reduction, the amount of their material compatible to viability of the individual occur due to geterokhromatinizirovanny X-chromosome and a heterochromatinic part of a Y-chromosome and therefore can be established by the analysis of a sex chromatin. Lack of X-chromatin in cells of the patient with a female phenotype is observed at a full agenesia of gonads at Shereshevsky's syndrome — Turner with a formula of a karyotype 45,X (see. Turner syndrome ) or at persons with a karyotype 46,XY at testicular feminization (see) and at chrome - an oozes-negative form of a dysgenesis of gonads. At a dysgenesis of ovaries of chromosomal genesis the frequency of occurrence and the sizes of a little body Burra depend on character of deviations in X-chromosome and correlate about a wedge. polymorphism of a disease. A little body Burra can have a normal amount, but be found seldom or even at all to be absent in separate fabrics (a mosaic form of a syndrome of Shereshevsky — Turner, a formula of a karyotype usually 46,XX/45, X); it can be reduced in comparison with norm (deletion of a short or long shoulder of X-chromosome, ring X-chromosome) or, on the contrary, increased (on a long shoulder of the H-isochromosome). A various wedge, forms of a testicular dysgenesis correlate with character of deviations in a Y-chromosome and have a different picture of Y-chromatin: from its absence or low contents (mosaicism with a formula of a karyotype 46,XY/45, X) before changes in size and a form (deletions of a long shoulder of an isochromosome, dicentric chromosomes). Researches P. x. at different forms of a true and false hermaphroditism are carried out only as approximate, for to-rymi the careful research of chromosomal complements shall follow.

At the disturbances of sexual development connected with increase in number of X-chromosomes in cells of patients additional little bodies Burra are found. Their number is defined by a formula n — 1 where n — total quantity of X-chromosomes at the individual. So, at a karyotype 47,XXX in cells of the woman two little bodies Burra are found, at a karyotype 48,XXXX — three little bodies Burra. Additional Y-chromosomes prove emergence in a cell of additional little bodies of Y (at a karyotype 47,XYY — two Y-little bodies, at a karyotype 48,XYYY — three Y-little bodies). At Klaynfelter's syndrome (see. Klaynfeltera syndrome ), when the Karyotype of the patient includes two or more X-chromosomes and one or more Y-chromosome, at the same time contain in somatic cells X-and Y-chromatin (on one little body of everyone at the most often found form of a syndrome with a formula of a karyotype 47,XXY).

A sex chromatin in the medicolegal relation

the Research P. x. in court. - medical practice it is made for the purpose of establishment of a sex of traces of blood, saliva and others biol, liquids, the pulled-out hair, traces prints of cells of fabrics and bodies, pieces of fabrics which can be found on site incidents, on various objects, clothes, a body of the victim and suspect of commission of crime, on tools of an injury, on vehicles, and also at detection of the burned corpses or parts of the dismembered corpses. P. is more rare x. investigate on purpose court. - medical establishments of a genetic gender of persons with anomalies of sexual development, using the practical standards.

For preparation of drugs from traces blood (see) and saliva (see) pieces of a subject carrier place in a test tube and fill in 0,5 — 40% (traces of blood) or 5 — 10% (traces of saliva) acetic to - that. Extract at the room temperature within several hours and, having removed pieces of a subject carrier, centrifuge. The deposit is transferred to a slide plate and dried up on air. From spots of blood on the objects which are not absorbing liquid (metal, glass, plastic, etc.), do scrapings which then process in the same way.

At a research hair (see) the root of a hair is placed on a slide plate and add 10 — 25% acetic to - that. After swelling separate and crush a hair follicle, deleting other parts of a hair.

From pieces of fabrics p bodies, if necessary previously having stood them before swelling in acetic to - those the corresponding concentration or in fiziol, solution, prepare gistol, drugs, smears or contact preparations. Traces imposings of cells, fabrics or bodies on tools of an injury wash away fiziol, solution, at the same time scratching out them. The small pieces of fabrics which are found in such traces crush microscopic needles. Would place in test tubes, centrifuge, from a deposit prepare gistol, drugs. It is reasonable to begin a research of drugs with identification of Y-chromatin since at its absence the same drugs can be used for identification of X-chromatin again. At a research consider only rather well remained unimpaired kernels of cells. In the analysis of traces of Y-chromatin blood define in kernels of lymphocytes since in neutrophils Y-chromatin in drugs from traces of blood of men can not come to light.

In the absence of the raised P.'s humidity x. can it is long to remain in the dried traces, and also in cells of a follicle of the pulled-out hair. High temperature (higher than 150 °) destroys kernels of cells and P. x. Considerable humidity within several days also leads to destruction of cells that makes impossible identification of a sex chromatin. Since conditions, in to-rykh are traces, can consistently change, crucial importance for establishment of suitability of traces of blood, saliva etc. for P.'s definition x. has a condition of the cells found in them and their kernels. In cells of the dried pieces of the fabrics which are not treated to action of moisture, P. x. the long time remains. In the whole corpses and in their large parts in the course of an autolysis and rotting within several days there is a destruction of cellular kernels. In the burned corpses a sex chromatin a nek-swarm time can remain in cells of deeply located bodies and fabrics.

At identification of a small number of the cells which kept kernels, investigated on P. x., for the purpose of establishment of statistical reliability of results use various mathematical methods of the analysis considering both total number of the found cells, and number of cells. containing X-or Y-chromatin.

Bibliography: Davidenkova E. F., the Berlin D. K. and Thousands-N yu to S. F. Clinical syndromes at anomalies of gonosomes, JI., 1973; Zakharov A. F. Chromosomes of the person, M., 1977; Kapustin A. V. Medicolegal diagnosis of a floor on sexual distinctions in cells, M., 1969; Laboratory and special methods of a research in forensic medicine, under the editorship of V. I. Pashkova and V. V. Tomilin, page 157, M., 1975; The Lubin S. I. and Antonova of S. N. Issledovaniye of Y-chromatin in traces of blood, Court. - medical examination, t. 18, No. 3, page 17, 1975; Fundamentals of cytogenetics of the person, under the editorship of A. A. Prokofieva-Belgovskoy, M., 1969; Methods in human cytogenetics, ed. by H. G. Schwarzacher a. U. Wolf, p. 207, B. and. lake, 1974; The sex chromatin, ed. by K. L. Moore, Philadelphia — L., 1966.

A. F. Zakharov; A. V. Kapustin (court.).