X chromatin testing can be used to diagnose. Chromosomal sex determination
Sex chromosomes (gonosomes, heterosomes) differ both in structure (length, centromere position, amount of heterochromatin) and in gene content.
Chromosome X- this is a submetacentric chromosome of medium size, part of group C). It is present in the somatic cells of individuals of both sexes: in duplicate in women with karyotype 46,XX and in one copy in men with karyotype 46,XY; and also in one copy in all eggs and 50% of sperm. Chromosome X is rich in euchromatic regions and contains 1336 genes, including: somatic genes, regulatory genes of feminization, structural genes of feminization, structural genes of masculinization. Thus, chromosome X is obligatory in the karyotype of a somatic cell of both female and male sexes.
Chromosome Y is a small acrocentric chromosome, part of group G; 2/3 of the distal q arm is represented by heterochromatin and is genetically inactive. Chromosome Y is represented by one copy in all somatic cells of male individuals with a karyotype of 46,XY and in 50% of sperm. It contains 307 genes, including: regulatory genes for masculinization (SRY + Tdf), genes providing fertility (AZF1, AZF2), several structural somatic genes and pseudogenes.
Morphological and genetic differences between the X and Y chromosomes, as well as differences in the number of X chromosomes in the karyotype, have caused genetic inequality between the sexes (women have a double dose of X chromosome genes compared to men. However, this inequality does not manifest itself, thanks to the compensation mechanism, as a result of which only one X chromosome remains functional in somatic cells of both men and women, namely:
In 46,XX cells, only one X chromosome is active;
In cells 46,XY – chromosomes X and Y are active;
In cells 47,ХХХ – only one chromosome X is active;
In 47,XXY cells, only one X chromosome and one Y chromosome are active;
In cells 48,ХХХY – only one chromosome X and one Y are active;
By heterochromatinization of one of the two chromosomes X and women, sex chromatin X is formed, and as a result of heterochromatinization of 2/3q of chromosome Y in males, sex chromatin Y is formed.
Sex chromatin X:
Represents the inactivated X chromosome in the form of facultative heterochromatin, in somatic cells 46,XX;
It is detected in the interphase nuclei of somatic cells in the form of a Barr body about 1 µm in size;
The Barr test is used to determine the number of X chromosomes in the karyotype in normal conditions and in the case of gnosomal aneuploidies;
Number of X chr. = number of Barr bodies + 1 (active X chr.);
46,XX – 1 Barr body;
46,ХY – Barr body is absent;
47,ХХХ – 2 Barr bodies;
47,XXY – 1 Barr body;
45,Х – Barr body is absent;
48,ХХХХ – 3 Barr bodies.
Sex chromatin Y:
2/3 of the Y q arm of the Y chromosome is represented, in the form of constitutive heterochromatin, in somatic cells 46,XY and sperm 23,Y;
It is detected in interphase cell nuclei in the form of an F (fluorescent) body about 1 µm in size;
The F test is used to identify the Y chromosome (prenatal sex determination);
Number of chr.Y = number of F bodies;
46,XX – no F body;
46,ХY – 1 F body;
47,ХYY – 2 F bodies;
47,XXY – 1 F body;
48,ХХYY – 2 F bodies;
46,X,i(Yp) – F body is missing;
46,X,i(Yq) – 1(0.5 µm) F body.
SEXUAL CHROMATIN SEXUAL CHROMATIN
areas of chromatin that determine the differences in interphase nuclei in individuals of different sexes, associated with the peculiarities of the structure or functioning of sex chromosomes. There are Y-P. X. (Y-chromatin) and X-P. X. (X-chromatin). Y-chromatin is the structural heterochromatin of the human Y chromosome, detected in the interphase nucleus using fluorochromes in ultraviolet light. X-chromatin, or Barr body, is a structure (0.7-1.2 µm) intensely stained with basic dyes, located in the nuclei different types cells of females, is normally formed by one of the two sex chromosomes of homogametic sex. This chromosome is spiralized and therefore inactive. Subject to availability more All X chromosomes are subject to this inactivation except one X chromosome. Therefore, the number of P. x. one less than the number of X chromosomes and serves as a diagnostic. sign when determining their number. A similar mechanism for the formation of P. x. found in most mammals.
.(Source: Biological encyclopedic dictionary." Ch. ed. M. S. Gilyarov; Editorial team: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected. - M.: Sov. Encyclopedia, 1986.)
See what "SEXUAL CHROMATIN" is in other dictionaries:
SEXUAL CHROMATIN- Fölgen is a positive body located in the nucleus. In higher mammals it occurs in females... Terms and definitions used in breeding, genetics and reproduction of farm animals
sex chromatin- Barr body. The X chromosome of female mammals is heterochromatinized during the process of lyonization and intensively stained during the analysis of interphase nuclei; identification of P.x. is the basis of the express method (i.e. without culturing cells and obtaining... ...
Sex chromatin- * palava hramatsin * sex chromatin condensed mass of chromatin (see), present in inactivated X chromosomes. Each X chromosome in the nuclei of mammals forms chromatin bodies in excess (. Late replicating X chromosome), which ... ... Genetics. Encyclopedic Dictionary
Sex chromatin, Barr body Heterochromatinized through the process of lyonization
A dense, staining body found in non-fused (interphase, see Interphase) cell nuclei in heterogametic (having X and Y sex chromosomes) animals and humans. P. x. divided into X chromatin, or Barr body (discovered in 1949 ... Great Soviet Encyclopedia
- (from the Greek chroma, gender chromatos color, paint), nucleoprotein threads that make up the chromosomes of eukaryotic cells. The term was introduced by W. Flemming (1880). In cytology, X. means the dispersed state of chromosomes in the interphase of the cell... ... Biological encyclopedic dictionary
chromatin-negative Klinefelter syndrome- A form of Klinefelter syndrome, in which sex chromatin (heterochromatinized Y chromosome) is absent in interphases (not detected by conventional staining methods) in the presence of a normal chromosome set 2n=46, XY. [Arefyev V.A.,... ... Technical Translator's Guide
Chromatin negative Klinefelter syndrome chromatin negative Klinefelter syndrome. Form of Klinefelter's syndrome
Chromatin, present only in female somatic cells and representing one inactivated X chromosome that remains in condensed form. A woman's somatic cells contain one active X chromosome. By gender... ... Medical terms
- (syn.: Barra body, X chromatin) a densely stained large area of X. triangular, round or rod-shaped, located on the periphery of the nucleus of a somatic cell of the female body; is a condensed X chromosome... Large medical dictionary
Often in gynecology and pediatric andrology there is a need to conduct a genetic examination of the patient. This method allows you to more reliably establish the causes of the disease, select the necessary course of treatment and determine prognosis for the development of the disease.
Sex chromatin - important indicator normal sexual development at the cellular level. Its diagnosis is necessary in cases where we're talking about about anomalies in the structure of the external genitalia. The study is also carried out when identifying diseases caused by chromosomal pathologies and in the presence of signs of impaired sexual development. The reason for this may be the lack of menstruation in girls and underdevelopment of the ovaries or decreased function in boys.
Sex chromatin was first discovered by scientist J. Bar in 1949. While examining the cat, he noticed a chromatin formation on the periphery of the nucleus. Subsequently, this important feature of female somatic cells was identified in most representatives of the order of mammals. Such bodies were not found in the male cells. The Barr corpuscle is a component of all women. And in some cases it has peculiar appendages (“ drumsticks"). Somatic cells are integral components of the human body. These include all cells of the body, except gametes. This discovery allowed us to expand our understanding of methods for determining sex in humans and mammals.
Availability in female body Barr bodies are explained by the presence of two X chromosomes in somatic cells. Moreover, only one of them is active. That is why female cells always contain a Barr body. This theory subsequently made it possible to identify anomalies in the development of the body. So, a cell with three chromosomes will have two bodies, with four - three, etc. Diagnosis of abnormal cell development can be used for both men and women. Since 1953, this discovery has been actively used to determine the exact developmental disorders.
Sex chromatin, or Barr body, looks like a dark mass of round, triangular or rod-shaped, which is located near the inner surface of the nuclear membrane. This is an inactive X chromosome, which in diameter does not exceed 1 micron. The detection of Barr bodies in 10-12% of the studied cells indicates positive sex chromatin. The research material is usually the epithelium of the mucous membrane of the cheek (inner surface), vagina, hair follicles and If the indicator does not exceed 5%, this indicates negative sex chromatin.
Sex chromatin determines differences in interphase nuclei in men and women. It is associated with the characteristics of functioning and their structure. There are two types of Barr body: Y and X. The first option is structural component Y chromosome and is detected mainly in men. For these purposes, fluorochrome using ultraviolet light is used. X chromatin (Barr body) is an inactivated X chromosome. Its deactivation occurs in the first weeks of intrauterine development and persists during mitotic division long time.
It should be noted that sex chromatin is a dynamic structure. It may vary depending on general condition body and cell metabolism. It is for this reason that examination is not recommended during use. hormonal drugs, in the first days after birth, after taking antibiotics and other medicines.
Today, based on the presence of sex chromatin, doctors determine the genetic sex of the unborn child and diagnose various clinical forms of gonadal dysgenesis and hermaphroditism. Tests to identify this component are widely used in forensic practice.
A number of disorders of somatosexual development of the human body, anatomical or functional defects of the gonads can be correctly recognized and classified, first of all, by determining the state of sexual chromatin, and then by assessing the karyotype (characteristic of an individual or a type of set of chromosomes). It is therefore necessary to begin with some basic information regarding the importance of cytogenetic studies in obstetrics and gynecology.
The influence of chromosomes on the sex of the child
The basis of numerous works on the study of sex chromatin was interesting data published by Bertram, which revealed differences between nuclei in cats nerve cells females and males.
Found by these authors in the cell nuclei of females cyanophilic chromatin clump , which differed in size and density from the other grains of the latter, was called sex chromatin by them. While in females this lump has the appearance of a plano-convex formation adjacent to the nuclear membrane, in males chromatin is almost never detected, since it is evenly distributed throughout the cell nucleus. Likewise, in women, in the resting nuclei of most oral epithelial cells, as well as a number of other areas, it was later possible to detect the presence of sex chromatin in the form of a single body; In men, sex chromatin is most often absent or occurs only occasionally.
The question of what determines the appearance of male and female individuals in the offspring genetically has long been resolved. The sex of the child is determined very early, already at the moment of fertilization, depending on which sperm penetrated the egg during the process of fertilization.
As you know, in humans there are two types of sperm. The nucleus of one group contains 23 chromosomes, including one sex chromosome, or X chromosome (gonosome), the rest are called autosomes. Another type of sperm also contains 23 chromosomes, but instead of the X chromosome it has a different sex chromosome. All female eggs therefore contain 22 autosomes plus the X sex chromosome, thus being completely identical in the number of chromosomes. When an egg is fertilized by a sperm with an X chromosome, a girl is born whose cells contain two sets of 22 autosomes plus 2 X chromosomes, i.e. a total of 46 chromosomes. When an egg fuses with a sperm containing a Y chromosome, a boy is born whose cell nuclei contain two sets of autosomes plus two sex chromosomes. The F chromosome, participating in sex determination, contributes to the formation of a male individual.
Figure 1. Example of normal fertilization and determination of female and male sex
To theoretically explain these facts, Lyon proposed a hypothesis, the content of which is briefly summarized as follows. If in early period During the development of the female embryo there are two active sex X chromosomes, then around the 16th day of embryonic life one of them is inactivated and takes the form of clumps of heterochromatin. It should be borne in mind that in a woman’s body there are two chromatins of different origins: one from the mother, the other from the father. When further inactivation occurs, it affects Xt in some cells and Xp in others (Z-paternel). Thus, in a woman’s body, even among cells located close to each other, a state of a peculiar mosaic of active Xt- and Xp-chromosomes arises. As a result of inactivation of a single chromosome.
Determination of sex chromatin in the clinic
The simplest and most widely used method is cytological examination sex chromatin in oral epithelial cells. Taking a scraping from the oral mucosa with a metal spatula, a smear is prepared from the resulting material, which is fixed in alcohol or in a mixture of alcohol and ether. The specimen is stained with hematoxylin and eosin and viewed under a microscope using an immersion objective. In preparations of smears from the oral cavity of men, sex chromatin is found only in 0.5-0.7% of cell nuclei; in women this percentage is 40-60.
Rice. 3. The mechanism of fertilization and sex determination according to E. Teter.a - determination of the female sex; b - male gender determination; 1 - egg; 2 - female and male embryos; 3 - the presence of sex chromatin (Fig. o) and its absence (Fig. b)
To obtain error-free results for determining sex chromatin, a number of laboratories resort to a more complex staining technique using a thionin solution. With such longer and more painstaking work, good results are obtained. X chromosomes in a number of embryonic cells with karyotype 45/X0, which corresponds to the so-called Shereshevsky-Turner syndrome; these cells lose viability, and the death of some of them during embryonic life leads to the appearance of somatosexual abnormalities, so often observed in this syndrome (low height, wing-shaped folds on the neck, etc.).
When stained, the cell nuclei are painted greenish, and their structure becomes very clear and sex chromatin is clearly highlighted, the presence of which can be easily established (Fig. 4). It is also possible to determine sex chromatin in blood smears taken by pricking the flesh of a finger.
The dried smear is stained with May-Grunwald reagent or Giemsa paint; then, after washing with water, it is dried at room temperature. Drugs are studied using immersion at 750-1500x magnification.
To establish sex chromatin, 500 neutrophil granulocytes must be examined; in men, no more than 6 leukocytes have additional segments (up to 1.5 microns in size) connected to the rest of the cell nucleus by a thread of karyoplasm. In genetically female individuals, for every 250 leukocytes examined, at least 6 or significantly more cells with additional lobules resembling “drumsticks” are found.
The forms of nuclear processes found in neutrophilic leukocytes are usually divided into three groups (Fig. 5).
Rice. 5. Different patterns of sex chromatin in smears taken from the oral cavity.Rice. 5. Various localizations of “drumsticks” in the nuclei of neutrophil leukocytes (according to E. Teter).
Group A - “drumsticks”, which look like small pear-shaped processes attached to one of the segments of the leukocyte nucleus with a thin, but clearly defined thread. They have a constant size and shape and are characteristic mainly of the genetically female sex. Group B is distinguished by the inconstancy of the shape of the processes detached from the neutrophil nucleus; sometimes there are several of them in one leukocyte and in appearance they are less similar to typical “drumsticks”. Although this group occurs in both sexes, it is more often found in males. Group C - “pseudo-drum sticks” - have a round or oval shape, are unevenly colored; their surface is often folded, they are connected to the leukocyte mass by a thick stalk. Group C occurs in both sexes, more often in men. Real female chromatin is a swollen clump connected to one of the leukocyte segments by a very thin stalk. The established presence of sex chromatin is generally considered a sign of female gender.
Anomalies
Currently Barr bodies are considered as the result of the spiralization of one of the two X chromosomes inherent in a woman. This spiralization, which occurs in cells outside of mitosis, leads to genetic inactivation of the sex chromosome. Since the only X chromosome in men does not coil, they usually do not have Barr bodies. They are also absent in women with a pathological set of XO chromosomes.
However, congenital sex anomalies are observed, which are characterized by the absence of sex chromatin in women, but the presence of a mosaic in the cell nuclei, when some cell nuclei contain only one X chromosome, while others have XY chromosomes. It is believed that such a mosaic is a consequence of the loss of the Y chromosome by one of the cells of the male embryo already in the early stages of its development. In such cases, although the external and internal genital organs are built according to the female type, during transection, rudiments of the gonad are found on one side, and on the other - a defective ovary, in which, due to the accumulation Leydig cells there is no spermatogenesis. The presence of a vagina, uterus, and oviducts indicates that the only gonad, the testis, did not secrete a sufficient number of inducers that could ensure complete regression of the Müllerian canal derivatives and masculinization of the reproductive tract, as a result of which the female reproductive system developed.
The previous view that two X chromosomes are required for the formation of sex chromatin has been revised and has not been confirmed. In women with karyotype 47/XXX, a study of sex chromatin revealed two Barr bodies; with chromosome set 48/XXX, the presence of three clumps of sex chromatin was established. In light of these data, it is currently accepted as a rule that the number of Barr bodies found in each cell is determined by the n - 1 rule, i.e., equal to the number of sex chromosomes found in it minus 1 (Fig. 6).
Rice. 6. Comparative studies of sex chromatin and chromosome set (each type of nuclear chromatin corresponds to two or more combinations of sex heterochromosomes (according to E. Teter).
However, there are exceptions. Thus, when studying fruits with a polyploid number of chromosomes and the presence of up to 6 X chromosomes in one cell, only one Barr body was determined. If women normally have two X chromosomes (one of paternal and one of maternal origin), one or the other can be inactivated. This spiralization and despiralization of the sex chromosome is one of the manifestations of the general ability of somatic cells to activate or inactivate individual genes or gene complexes located on the same chromosome, which plays an important role in the process of cell development and differentiation.
It should be remembered that males may have XXX chromosomes, and in such cases, sex chromatin can be detected in the cells of their tissues, which does not yet allow them to be considered female. At the same time, the absence of sex chromatin is not yet evidence of the presence of sex chromosomes of the male type (XY), since during gonadal dysgenesis the chromosome composition may be XO, and then female nuclear chromatin is not found in tissue cells (Fig. 7, a, b). Therefore, the following terminology is currently used:
- The person being examined has a positive type of nuclear chromatin (that is, characteristic Barr bodies are found in the cells of his tissues);
- The person being examined is negative.
Sometimes it is possible to differentiate chromosomes, the morphological isolation of which is sometimes very difficult. Mention should also be made of the electron microscopic study of human chromosomes. Due to the huge increase in the number of studies using the above technical methods and a significant number of individual nomenclatures from a number of authors, it became necessary to develop a unified nomenclature for the chromosome set, which was done at the conference of cytogeneticists in Denver.
Rice. 7 Pathological result of fertilization due to the phenomenon of inseparability. 1- using the example of Shereshevsky-Turner syndrome; b - using the example of Kleinfelter syndrome
Type of nuclear chromatin (if at least 40-60% of its tissue cells do not contain Barr bodies). It should not be forgotten, however, that individuals with a male type of sex chromosomes may have sex chromatin in 0.5-0.7% of cases.
Among newborn boys, the number of chromatin-positive ones is on average 1.7 per 1000. The number of chromatin-negative girls is 0.3 per 1000. For every 1000 female newborns, there is one case with a karyotype of 47 XXX (the so-called superwomen).
Sex chromatin was first discovered by scientist M. Barr in 1949. Subsequently this important feature female somatic cells were identified in representatives of the mammalian order. Such bodies were not found in the body of males. This discovery allowed us to expand our understanding of methods for determining sex and people.
Sex chromatin (Barr bodies) is part of all somatic cells of women. Somatic cells include all cells of the body except gametes. The Barr body is a dark, triangular, round, rod-shaped mass located near the inner surface of the nuclear membrane. The presence of sex chromatin in the female body is explained by the presence of two X chromosomes in somatic cells; only one of them is active. Essentially, the Barr body is an inactivated X chromosome.
Another type of chromatin was subsequently discovered in the body of men - Y-chromatin. It is a structural region of the Y chromosome that is found in the interphase nucleus. The difference in interphase nuclei in the body of men and women is due to the type of sex chromatin, which is related to the characteristics of the functions of the reproductive systems.
Sex chromatin analysis
The discovery of sex chromatin made it possible to identify anomalies in the development of an organism, for example, a cell with 3 chromosomes has 2 bodies, with 4 - 3, etc. Since 1953, a similar research method has been actively used to determine the exact number of X chromosomes in people with developmental disorders. Based on the presence of sex chromatin, the genetic sex of the unborn child is determined and clinical forms are diagnosed hereditary diseases.
Sex chromatin tests are used in forensic practice. The biological material is the epithelium of the vagina, buccal mucosa (inner surface), amniotic fluid, and hair follicles. Detection of sex chromatin in 10-12 percent of the cells examined is a positive indicator. If it does not exceed 5%, this will indicate negative sex chromatin.
Sex chromatin is a dynamic structure that can change depending on cell metabolism and the general condition of the body, therefore it is not recommended to conduct examinations in the first days after birth, during the use of hormonal drugs, antibiotics and some other drugs.