SEXUAL CHROMATIN- a section of the nucleus of a somatic cell in interphase, which is a condensed sex chromosome; As a result of condensation of the X chromosome, X-chromatin is formed, and condensation of the Y chromosome results in Y-chromatin. In people with normal chromosome composition (see Karyotype), the somatic cells of women contain X-chromatin, and the somatic cells of men contain Y-chromatin. Based on the presence of these formations, the genetic sex of an individual can be determined (see Gender), which finds practical application in the diagnosis of various wedges, forms of testicular and ovarian dysgenesis (see Gonadal dysgenesis), an indicative study of individuals for false - pseudohermaphroditism (see) or true hermaphroditism (see), in forensic medicine. practice, etc.
X-chromatin (the so-called Barr body), as a female-specific cytol, was first described by M. Barr and E. G. Bertram in 1949; one of the two X chromosomes in early embryogenesis is genetically inactivated (heterochromatinized) and remains condensed throughout the interphase period of the life of the somatic cell. Decondensation of the heterochromatinized X chromosome in a somatic cell does not mean its genetic activation. The second X chromosome in a female cell and the X chromosome in a male somatic cell do not form X chromatin. Y chromatin is formed by part of the long arm of the Y chromosome; it consists of heterochromatin, condensed in the interphase nucleus and capable of intense fluorescence after staining with quinine and other fluorochromes (see). The fluorochrome test for determining the sex of cells based on Y-chromatin was first proposed by T. Caspersson in 1970.
When determining the genetic sex of an individual, his cells are examined for both X- and Y-chromatin. For this, cellular material is obtained (its source can be a wide variety of tissues, although those that do not require preliminary in vitro cultivation are preferable; to determine X-chromatin, smears from the buccal mucosa are most often used, less often from the vaginal mucosa, as well as cells of hair follicles; amniotic cells are used for prenatal diagnosis of fetal sex. The content of Y-chromatin, in addition to the listed tissues, can also be determined in spermatozoa. An excellent material for the analysis of X- and Y-chromatin are single-layer cell cultures, usually fibroblasts. In cultured Y-chromatin is clearly visible in blood lymphocytes. The preparations are fixed before drying them in air, usually fixed with methanol or a mixture of ethanol and acetic acid (in a ratio of 3:1) or with ethanol alone. Staining methods for identifying X- and Y-chromatin are different X-chromatin is better revealed when staining preparations with basic non-fluorescent dyes: basic fuchsin, thionin, acetoorcein, toluidine blue, etc. The stained preparations are dried and studied with oil immersion in transmitted light. Y-chromatin is detected by staining preparations with fluorochromes - derivatives of acridine orange: akrikhine, akrikhin-mustard, akrikhin-propyl. The preparations are placed in a special buffer solution and examined in ultraviolet light using a fluorescent microscope (see). The analysis is carried out on disconnected, spread out cells. Tissue sections for determining P. x. used only when it is impossible to obtain smears or imprint preparations of an organ section.
The Barr body in a normal diploid cell has the shape of a triangle, round or even rod-shaped formation, the average linear size of which is 1 micron. Very often, the Barr body is located on the periphery of the nucleus and often comes into contact with the nuclear envelope. Size, shape, position in the nucleus and dense coloration make it possible to distinguish X-chromatin from clumps of condensed chromatin of other chromosomes. The frequency with which X-chromatin occurs in cells depends on the state of the body (hormonal status, physical activity, etc.)* It is low in newborn girls in the first 2-3 days of life. In a sexually mature woman, the frequency of occurrence of X-chromatin fluctuates at different periods of the menstrual cycle, varies in different tissues and never reaches 100%. In cells of the buccal mucosa, X-chromatin is found in 25-60% of cells, in fibroblasts cultured in vitro - in 40-80% of cells, in uncultured amniotic cells in approximately 5% of cells. In granulocytes, X-chromatin has the appearance of a drumstick; the low detection rate (1.5-5%) and the difficulty of differentiating this formation from other nuclear structures have limited the practical dissemination of this test. In polyploid cells, the number of Barr bodies is a multiple of the number of diploid sets of chromosomes. In men, clumps of chromatin cytologically similar to X-chromatin are found in approximately 1% of cells.
The size of Y-chromatin in normal diploid cells varies greatly between individuals, which is associated with large fluctuations in the length of the Y chromosome itself. When diagnosing sex using Y-chromatin, it should be remembered that there are individuals with either an insignificant amount of heterochromatin in the Y-xpo-mosome or completely devoid of heterochromatin, and the non-detection of Y-chromatin in such individuals is not a fact that denies their belonging to the male sex. In most men, Y-chromatin appears as a relatively large (0.3-1 µm), brightly luminous formation (body), usually round in shape; in individual cells it may have a double structure or be somewhat diffuse. At the periphery of the cell nucleus, the Y body is located less frequently than the Barr body. The nucleus contains brightly glowing clumps of chromatin from other chromosomes, which are usually easy to distinguish from the Y body. The frequency of occurrence of Y-chromatin varies significantly in different tissues. In the cells of the buccal mucosa it is found in 20-80% of cells, in hair follicle cells in 70-90%, in peripheral blood lymphocytes in 60-87% of cells. Fluorescent bodies similar to the Y-body in a woman's cells (autosomal heterochromatin) are found in approximately 5% of cells. In women pregnant with a male fetus, the cells of the latter can penetrate into the mother's bloodstream. They are detected by the presence of Y-chromatin. To determine genetic sex using Y-chromatin, it is recommended to look at at least 50 cells.
Practical application of the test for P. x. in two ways. This test is used to determine the sex of an individual from his cells, when either the individual himself is not available for research (prenatal diagnosis of the sex of the fetus, forensic medical examination, etc.), or in cases where a mass check of phenotypic (passport) compliance is carried out ) genetic sex (for example, when examining women at sports competitions). Determination of the sex of the fetus in utero is carried out if a hereditary disease linked to sex is suspected (hemophilia, some forms of muscular dystrophy, etc.), in order to prevent the birth of a terminally ill child.
When examining patients with wedge. manifestations of impaired sexual differentiation and in other cases when an accurate description of the state of the sex chromosomes is necessary, regardless of the results of the analysis for P. x. resort to chromosomal analysis (see Chromosomes).
Especially often the definition of P. x. used for preliminary diagnosis of abnormalities in the number or structure of sex chromosomes when the subject has disorders of sexual development. Simplicity and speed of execution make it possible to use the test for P. x. during mass examination of newborns and other children to identify sex chromosome abnormalities. The final diagnosis is made after studying the chromosome set (see). Deviations in the sex chromosome system towards a decrease in the amount of their material, compatible with the viability of the individual, occur due to the heterochromatic X chromosome and the heterochromatic part of the Y chromosome and therefore can be established by analyzing sex chromatin. The absence of X-chromatin in the cells of a patient with a female phenotype is observed with complete agenesis of the gonads in Shereshevsky-Turner syndrome with a karyotype formula of 45,X (see Turner syndrome) or in individuals with a karyotype of 46,XY with testicular feminization (see) and with chromium -tin-negative form of gonadal dysgenesis. With ovarian dysgenesis of chromosomal origin, the frequency and size of the Barr body depend on the nature of the abnormalities in the X chromosome and correlate with the wedge. polymorphism of the disease. The Barr body may be of normal size, but rarely found or even completely absent in certain tissues (mosaic form of Shereshevsky-Turner syndrome, karyotype formula is usually 46.XX/45.X); it can be reduced compared to the norm (deletion of the short or long arm of the X chromosome, ring X chromosome) or, conversely, increased (along the long arm of the X isochromosome). Various wedges and forms of testicular dysgenesis correlate with the nature of deviations in the Y-chromosome and have a different picture of Y-chromatin: from its absence or low content (mosaicism with the karyotype formula 46,XY/45,X) to changes in size and shape (deletions of the long arms of isochromosomes, dicentric chromosomes). Research on P. x. for various forms of true and false hermaphroditism, they are carried out only as indicative ones, which should be followed by a thorough study of chromosome sets.
In cases of disorders of sexual development associated with an increase in the number of X chromosomes, additional Barr bodies are found in the cells of patients. Their number is determined by the formula n - 1, where n is the total number of X chromosomes in an individual. Thus, with a karyotype of 47.XXX, two Barr bodies are found in the woman’s cells, with a karyotype of 48.XXXX - three Barr bodies. Additional Y chromosomes manifest themselves by the appearance of additional Y bodies in the cell (with a karyotype of 47,XYY - two Y-bodies, with a karyotype 48,XYYY - three Y-bodies). In Klinefelter syndrome (see Klinefelter syndrome), when the patient's karyotype includes two or more X chromosomes and one or more Y chromosomes, somatic cells simultaneously contain X and Y chromatin (one body of each in the most common form of the syndrome with karyotype formula 47,XXY).
Sex chromatin in forensic medicine
Study of P. x. to the medical court practice is carried out in order to establish the gender of traces of blood, saliva and other biol, liquids, torn hair, traces-imprints of tissue cells and organs, pieces of tissue that can be found at the scene of an incident, on various objects, clothing, the body of the victim and suspect committing a crime, on instruments of injury, on vehicles, as well as upon discovery of charred corpses or parts of dismembered corpses. Less often P. x. investigated for the purpose of forensic medicine. establishing genetic sex in individuals with anomalies of sexual development using generally accepted methods.
To prepare preparations from traces of blood (see) and saliva (see), pieces of the carrier object are placed in a test tube and filled with 0.5-40% (traces of blood) or 5-10% (traces of saliva) vinegar. Extract at room temperature for several hours and, after removing pieces of the carrier object, centrifuge. The sediment is transferred to a glass slide and dried in air. Scrapings are made from blood stains on objects that do not absorb liquid (metal, glass, plastic, etc.), which are then processed in the same way.
When examining hair (see), the hair root is placed on a glass slide and 10-25% vinegar is added. After swelling, the hair follicle is separated and crushed, removing the remaining parts of the hair.
From pieces of tissue and organs, if necessary, having previously kept them until swelling in acetic acid of the appropriate concentration or in physiol solution, prepare histol, preparations, smears or imprint preparations. Traces of the imposition of cells, tissues or organs on the instruments of injury are washed off with physiol, solution, while scraping them off. Small pieces of tissue found in such marks are crushed with dissecting needles. The scrapings are placed in test tubes, centrifuged, and histol and preparations are prepared from the sediment. It is advisable to begin the study of drugs with the detection of Y-chromatin, since in its absence the same drugs can be used again to detect X-chromatin. During the study, only sufficiently well-preserved intact cell nuclei are taken into account. When analyzing traces of blood, Y-chromatin is determined in the nuclei of lymphocytes, since in neutrophils, Y-chromatin may not be detected in preparations from traces of blood from men.
In the absence of high humidity P. x. can persist for a long time in dried traces, as well as in the follicle cells of torn hair. High temperatures (above 150°) destroy cell nuclei and P. x. Significant humidity for several days also leads to cell destruction, which makes it impossible to detect sex chromatin. Since the conditions in which traces are found can change sequentially, this is crucial for establishing the suitability of traces of blood, saliva, etc. for determining P. x. has the state of the cells and their nuclei found in them. In the cells of dried pieces of tissue that are not exposed to moisture, P. x. persists for a long time. In whole corpses and in their large parts, during the process of autolysis and decay, destruction of cell nuclei occurs over several days. In charred corpses, sex chromatin can remain for some time in the cells of deeply located organs and tissues.
When identifying a small number of cells that have retained their nuclei and are studied for P. x., in order to establish the statistical reliability of the results, various mathematical methods of analysis are used, taking into account both the total number of detected cells and the number of cells. containing X- or Y-chromatin.
Bibliography: Davidenkova E. F., Berlinskaya D. K. and Thousand Yu to S. F. Clinical syndromes with abnormalities of sex chromosomes, JI., 1973; Zakharov A.F. Human chromosomes, M., 1977; Kapustin A.V. Forensic medical diagnosis of sex based on sexual differences in cells, M., 1969; Laboratory and special research methods in forensic medicine, ed. V. I. Pashkova and V. V. Tomilin, p. 157, M., 1975; Lyubinskaya S.I. and Antonova S.N. Study of Y-chromatin in traces of blood, Forensic Med. examination, vol. 18, no. 3, p. 17, 1975; Fundamentals of human cytogenetics, ed. A. A. Prokofieva-Belgovskaya, M., 1969; Methods in human cytogenetics, ed. by H. G. Schwarzacher a. U. Wolf, p. 207, B. a. o., 1974; The sex chromatin, ed. by K. L. Moore, Philadelphia - L., 1966.
A. F. Zakharov; A. V. Kapustin (court).
This phenomenon is called the S T Y A R T A rule. For example, if the karyotype is 47, XXX, then three X chromosomes minus one equals two Barr bodies. The presence of sex chromatin in men, as well as the presence or absence of additional Barr bodies in women, is characteristic of disorders in the sex chromosome system.
An increase in the number of Y chromosomes leads to an increase in fluorescent bodies in interphase nuclei, called Y chromatin.
An express method for determining sex chromatin in scrapings of the buccal epithelium of the buccal mucosa has been developed. The scraping material obtained with a spatula is transferred to a glass slide and stained with a 1% acetoarsein solution, covered with a coverslip and examined using a light microscope.
Sex chromatin determination is used for:
- Timely determination of sex in resolving issues of hereditary sex-linked diseases,
- Express diagnostics of chromosomal diseases associated with disruption of the sex chromosome complex. Klinefeltera 47, ХХУ. 48, XXXY, Turner 45, XO, Morris 46, XY - female phenotype, triplo - X - superwoman 47, XXX, disomy on the Y chromosome 47, XXXY. The ability to detect mosaicism by sex chromosomes – gynandromorphism - XXY/XX, both female and male characteristics are manifested. The most diverse forms of karyotypes XY/XO, XX/XO, XXX/XO, XX/XXX, and triple mosaics XO/XX/XXX have been described.
- Determination of sex in forensic medicine
- In oncology, to identify a tumor by sex chromatin and select the correct hormonal treatment
The cytogenetic method is used for:
- diagnostics of chromosomal and genomic diseases
- studying chromosomal and genomic mutations
- determination of sex in case of violation of sexual differentiation of the phenotype
- study of sex chromatin
Somatic cell genetics method
This method involves cultivation, cloning, hybridization and selection of somatic cells. CLONING – obtaining descendants (a large number of cells) from one cell through division. Cloned cells used to obtain a large number of cells for chromosomal analysis, to study the characteristics of metabolism, to quantitatively account for mutations, to prove the heterogeneity of cell populations.
Selection in somatic cell genetics they are used to select mutants for resistance, auxotrophy. The selection of resistance mutants is based on their survival in the presence of some lethal factor. The selection of auxotrophic cells is based on their ability to use strictly defined substances for their growth that are not synthesized by the cell.
By hybridization the localization of genes in chromosomes is established. Hybridization is based on the fusion of co-cultured cells of two different types. Hybrid cells or heterokaryons, contain nuclei with chromosome sets of two different species, for example, human and mouse, human and rat, human and Chinese hamster. The genotypes of such cells are in a state of imbalance and therefore, during cell division, heterokaryons usually lose some chromosomes. In different hybrid cells, chromosomes of the same type are lost. In human-mouse hybrid cells, human chromosomes gradually disappear. The gradual loss of human chromosomes can ultimately lead to the retention of a single chromosome. Thus, the preservation of human chromosome 9 in a human-mouse hybrid cell made it possible to establish that in response to the introduction of the virus, the cells of this clone began to produce interferon. Therefore, it was established that the gene responsible for the synthesis of interferon is located on chromosome 9.
Modeling methods
Two methods have been developed: biological and mathematical modeling. With the help of these methods, various problems are solved, which are important both for the development of the theoretical foundations of human genetics and for practical medical and biological consulting.
Biological modeling – This is the use of animals that have inherited anomalies corresponding to human anomalies.
Used in genetics for:
1. studying the pathogenesis of hereditary diseases.
2. development of methods for their treatment.
Math modeling– based on the use of computer technology. Using this method we study:
1. The spread of mutations in populations under different conditions is the action of selection;
2. The influence of experimental evolutionary factors in different combinations on the gene pool of populations during the spread of hereditary pathology.
Twin method
This is a method of studying genetic patterns in twins. It was first proposed by F. Galton in 1875. The twin method makes it possible to determine the contribution of genetic (hereditary) and environmental factors (climate, nutrition, training, upbringing, etc.) in the development of specific traits or diseases in humans. When using the twin method, a comparison is made:
1) monozygotic (identical) twins - MB with dizygotic (fraternal) twins - DB;
2) partners in monozygotic pairs with each other;
3) data from the analysis of a twin sample with the general population.
Monozygotic Twins are formed from one zygote, which is divided into two (or more) parts at the cleavage stage. From a genetic point of view they are identical, i.e. have the same genotypes. Monozygotic twins are always the same sex. They have one placenta.
A special group among MB consists of unusual types of twins: two-headed (as a rule, non-viable), caspophagous ("Siamese twins"). The most famous case is the Siamese twins, Chapg and Eig, born in 1811 in Siam (now Thailand). They lived for 63 years, were married to twin sisters; Chang fathered 10 and Eng fathered 12 children. When Chang died of bronchitis, Eng died 2 hours later. They were connected by a fabric bridge about 10 cm wide from the sternum to the navel. It was later determined that the bridge connecting them contained liver tissue connecting the two livers. Any surgical attempt to separate the brothers was unlikely to have been successful at that time. More complex connections between twins are now being severed.
Dizygotic twins develop when two eggs are simultaneously fertilized by two sperm. Naturally, dizygotic twins have different genotypes. They are no more similar to each other than brothers and sisters, because... have about 50% identical genes.
The overall incidence of twin births is approximately 1%, of which about 1/3 are monozygotic twins. It is known that the number of births of monozygotic twins is similar in different populations, while for dizygotic twins this figure varies significantly. For example, in the United States, dizygotic twins are born more often among blacks than whites. In Europe, the incidence of dizygotic twins is 8 per 1000 births. However, in some populations there are more of them. The lowest incidence of twin births is found in Mongoloid populations, especially in Japan. It is noted that the frequency of congenital deformities in twins is usually higher than in singletons. It is believed that multiple births are genetically determined. However, this is only true for dizygotic twins. Factors influencing the incidence of twin births are currently poorly understood. There is evidence showing that the likelihood of having dizygotic twins increases with the age of the mother, as well as the birth order. The influence of maternal age is probably explained by an increase in gonadotropin levels, which leads to an increase in polyovulation. There is also evidence of a decline in the incidence of twin births in almost all industrialized countries.
The twin method includes diagnostics of zygosity of twins. IN The following methods are currently used to: establish it.
1. Polysymptomatic method. It consists of comparing a pair of twins based on external characteristics (shape of eyebrows, nose, lips, ears, hair color, eyes, etc.). Despite its obvious convenience, this method is to a certain extent subjective and may produce errors.
2. Immunogenetic method. More complex, it is based on the analysis of blood groups, blood serum proteins, leukocyte antigens, sensitivity to phenylthiocarbamide, etc. If both twins have no differences in these characteristics, they are considered monozygotic.
For monozygotic twins, the probability of similarity in all respects is equal.
3. A reliable criterion for the zygosity of twins is survival rate
pieces of leather. It has been established that in dizygotic twins such a transplant always ends in rejection, while in monozygotic pairs there is a high graft survival rate.
4. Dermatoglyphics method consists of studying the papillary patterns of the fingers, palms and feet. These signs are strictly individual and do not change throughout a person’s life. It is no coincidence that these indicators are used in criminology and forensic medicine to identify individuals and establish paternity. The similarity of dermatoglyphic parameters in monozygotic twins is significantly higher than in dizygotic twins.
5. Twin method on It also includes a comparison of groups of mono- and dizygotic twins according to the trait being studied.
If any sign occurs in both twins of the same pair, then it is called concordant, if one of them has, then the pair is a twin ov is called discordant(concordance is the degree of similarity, discordance is degree of difference).
When comparing mono- and dizygotic twins, the pairwise concordance coefficient is determined, indicating the proportion of twin pairs. in which the studied trait manifested itself in both partners. The concordance coefficient (K p) is expressed in fractions of a unit or as a percentage and is determined by the formula:
Кп = С\С+Д where С is the number of concordant pairs. D - number of discordant pairs.
Comparison of pairwise concordance in mono- and dizygotic twins provides an answer to the relative role of heredity and environment in the development of a particular trait or disease. In this case, we proceed from the assumption that the degree of concordance is significantly higher in monozygotic than in dizygotic twins if hereditary factors have a dominant role in the development of the trait.
If the value of the concordance coefficient is approximately close in monozygotic and dizygotic twins, it is believed that the development of the trait is determined mainly by non-genetic factors, i.e. environmental conditions.
If both genetic and non-genetic factors are involved in the development of the trait under study, then certain intrapair differences are observed in monozygotic twins. At the same time, the differences between mono- and dizygotic twins in terms of the degree of concordance will decrease. In this case, it is believed that there is a hereditary predisposition to the development of the trait.
To quantify the role of heredity and environment in the development of a particular trait, various formulas are used.
Most often they use the heritability coefficient, which is calculated using the formula:
N = KMB - KDB(in percent) or (in fractions of a unit),
where H is the heritability coefficient. K is the coefficient of pairwise concordance in a group of monozygotic (MB) or dizygotic (DB) twins.
Depending on the value of H, the influence of genetic and environmental factors on the development of the trait is judged. For example, if the H value is close to 0, it is considered that the development of the trait is due only to environmental factors. With an H value from 1 to 0.7, hereditary factors have a dominant role in the development of a trait or disease - these are blood groups, eye color, Rh factor, and the average H value from 0.4 to 0.7 indicates that the trait develops under the influence of environmental factors in the presence of a genetic predisposition.
For example, the concordance rate for schizophrenia in MB is 70%, and in DB it is 13%. We calculate using the formula H = KMB – KDB / 100 – KDB = 70 -13 \ 100 – 13 = 0.65 or 65%. In this case, genetic factors predominate, but environmental conditions also play a significant role.
Using the twin method, the importance of genotype and environment in the pathogenesis of many infectious diseases was revealed. Thus, in case of measles and whooping cough, infectious factors are of leading importance, and in case of tuberculosis infection, the genotype has a significant influence. Twin studies may help answer on such questions as: the influence of hereditary and environmental factors on human life expectancy, the development of talent, sensitivity to drugs. In clinical pharmacology, there is no more effective method for evaluating the effects of new drugs and treatment regimens than comparing therapeutic results in identical twins. They also evaluate the effectiveness of various pedagogical techniques in the learning process.
Biochemical methods
Biochemical indicators reflect the essence of the disease more adequately than clinical symptoms. These methods are aimed at identifying the biochemical phenotype of an organism. They play a leading role in the diagnosis of monogenic hereditary diseases. The principles of biochemical diagnostics changed at different stages of genetic development:
- until the 50s - they looked for metabolites in urine (alkaptonuria, phenylketonuria);
- 50-70s – identification of enzymopathies and metabolites;
- since the 70s - squirrels.
Currently, all these objects are the subject of biochemical research.
Since there are a lot of biochemical methods, therefore, when using them there must be a certain system; the examination scheme is based on:
· clinical picture of the disease;
· genealogical information;
· gradual elimination of certain classes of diseases (sifting method).
Biochemical methods are multi-stage.
Objects of biochemical research:
ü plasma and serum;
ü formed elements of blood;
ü cell cultures (fibroblasts, lymphocytes).
When using the sieving method in biochemical diagnostics, the following levels are distinguished: primary and clarifying.
Purpose of primary diagnosis– identification of healthy individuals and selection of individuals for subsequent diagnosis. Urine and a small amount of blood are used at this stage.
Primary biochemical diagnostic programs are mass and selective.
- Barr body (X-sex chromatin) is an inactive X chromosome folded into a dense (heterochromatic) structure, observed in the interphase nuclei of somatic cells of female placental mammals, including humans. Paints well with basic dyes.
Of the two X chromosomes in the genome, either one can be inactivated at the beginning of embryonic development; the choice is made randomly. In the mouse, the exception is the cells of the germinal membranes, also formed from the tissue of the embryo, in which exclusively the paternal X chromosome is inactivated.
Thus, in a female mammal that is heterozygous for any trait determined by the X chromosome gene, different alleles of this gene operate in different cells (mosaicism). A classic visible example of such mosaicism is the coloration of tortoiseshell cats - in half of the cells the X chromosome with the “red” is active, and in half - with the “black” allele of the gene involved in the formation of melanin. Tortoiseshell cats are extremely rare and have two X chromosomes (aneuploidy).
In humans and animals with aneuploidy, which have 3 or more X chromosomes in their genome (see, for example, Klinefelter syndrome), the number of Barr bodies in the nucleus of a somatic cell is one less than the number of X chromosomes.
Related concepts
Chromosomal rearrangements (chromosomal mutations, or chromosomal aberrations) are a type of mutation that changes the structure of chromosomes. The following types of chromosomal rearrangements are classified: deletions (loss of a chromosome section), inversions (change in the reverse order of the genes of a chromosome section), duplications (repetition of a chromosome section), translocations (transfer of a chromosome section to another), as well as dicentric and ring chromosomes. Isochromosomes are also known to have two identical arms. If perestroika changes...
The process of implementing a genetically determined program for the formation of a specialized phenotype of cells, reflecting their ability to perform certain profile functions. Differentiation changes cell function, size, shape and metabolic activity.
Linked inheritance is the phenomenon of correlated inheritance of certain states of genes located on the same chromosome.
Conjugation in ciliates is a sexual process of ciliates, accompanied by the transfer of nuclei between the cells of partners during their direct contact. The presence of such a peculiar sexual process is a unique feature of ciliates. The sexual process in ciliates, unlike the sexual process in the usual view, is not accompanied by the formation of gametes, therefore they do not have a zygote. In addition, conjugation of ciliates is not accompanied by reproduction, that is, an increase in the number of cells, therefore conjugation...
Cajal body (CB) is a formation in the cell nucleus, present in some nuclear organisms. The typical size of Cajal bodies is 1-2 μm, and one cell can contain from 0 to 10 MCs. Many types of cells do not have MCs, but MCs are present in the nuclei of neurons and cancer cells. The main function of Cajal bodies is the processing of small nuclear and small nucleolar RNAs, as well as the assembly of ribonucleoprotein complexes.
Paraspeckles, or paraspeckles, are a class of nuclear bodies located in the interchromatic space of the cell nucleus in mammalian cells. They are composed of proteins and RNA and are formed by the interaction of a long non-coding RNA, known as NEAT1/Men ε/β, and proteins of the DBHS (Drosophila Behavior Human Splicing) family, namely P54NRB/NONO, PSPC1 and PSF/SFPQ. Paraspeckles play an important role in the regulation of gene expression, ensuring retention of RNA molecules containing...
Epistasis is a type of gene interaction in which the expression of one gene is influenced by another gene (genes) that is non-allelic to it. A gene that suppresses the phenotypic manifestations of another is called epistatic (inhibitor, suppressor); a gene whose activity is altered or suppressed is called hypostatic.
Technological map of the practical lesson
Subject " Genetics of sex in humans. Barr bodies and their diagnostic value».
Biology teacher of GBPOU KKBMC - Lina Petrovna Chertkova
Duration 90 min (2 hours)
Objectives of the training session:
Educational:consolidate, expand and deepen knowledge on the topic.
Developmental: continue to develop the ability to apply theoretical knowledge in practice; promote the development of logical thinking; ability to analyze and highlight the main thing.
Educational: promote feelingsconscious responsibility for your health and the health of others.
Requirements for skills and knowledge:
Know:
structure and types of metaphase chromosomes, karyotyping, Denver classification of chromosomes.
Be able to:
Reveal morphological differences between individual chromosomes and groups of chromosomes;
Use knowledge of the cytological principles of heredity to solve problems;
Know the algorithm for solving problems
Educational technologies: technology differentiated approach to learning; personal development,problem-situational learning, information and communication technologies.
Teaching methods and techniques:explanatory and illustrative (explanations, instructions); methods that determine the logic of teaching: (comparison, generalization, systematization); methods that stimulate and motivate educational and cognitive activity (problem solving), partly search methods.
Means of education:
Educational and visual materials, handouts: methodological instructions for the practical lesson.
Technical teaching aids: handouts on the topic· drawing: “Chromosome set of a man and a woman; diagrams of differentially colored chromosomes.
Literature:
- Medical genetics: textbook / ed. N P. Bochkova. M.: GEOTAR-Media, 2014.
- Lecture notes
Additional sources:
1. Akulenko L.V., Ugarov I.V. Biology with the basics of medical genetics. Moscow, ed. group "GEOTAR-Media", 2011
2. Internet resource: www.msu-genetics.ru
Interdisciplinary connections:human anatomy and physiology, biology.
Intrasubject connections between sections:“Cytological and biochemical bases of heredity”, “Methods for studying human heredity and variability in normal and pathological conditions”, “Heredity and pathology”.
Basic concepts:karyotype, chromosome, metacentric, submetacentric and acrocentric chromosomes, chromatin, euchromatin, heterochromatin, sex chromatin (Bar bodies).
Chronological map of the lesson
Stages of a training session | Equipment use | Time |
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Organizing time. | checking those present, students’ appearance, checking students’ readiness for class. | 2 minutes |
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Goal setting, initial motivation. | announcement: topic, its problematic issues; objectives of the lesson. | 2 minutes |
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Determination of the initial level of knowledge. | Terminological dictation (work on control sheets) | 5 minutes |
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The teacher controls the students' work in their notebooks. | 60 min |
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Checking notebooks. | The teacher checks the correctness of assignments | 5 minutes |
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Generalization, systematization of knowledge | 10 min |
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Summarizing. | Grading with teacher comments | 5 minutes |
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Homework | Preparing for the next lesson. | 1 min |
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Total | 90 min |
Lesson notes
- Organizing time
- Announcement of the topic and goals of the lesson, initial motivation and updating.
Introductory speech from the teacher:The problem of the origin of sexual differences, the mechanism of sex determination and the maintenance of a certain sex ratio in a population is fascinating and at the same time very important for theoretical biology. Questions about why boys and girls are born in approximately equal numbers, and why the same sex ratio is observed in most animals from generation to generation, could not help but worry scientists. Many guesses were made, but none of them received scientific confirmation until the development of genetics and cytology revealed the mechanism of inheritance and sex determination.
Formulation of the problem.
Most animals and dioecious plants are dioecious organisms, and within a species the number of males is approximately equal to the number of females. In other words, every species that has a clear division into males and females has a 1:1 ratio.
What determines the birth of male and female individuals? How to explain this phenomenon?
It can be proposed that one sex produces two types of gametes (heterozygous), and the other produces one (homozygous).
The sex of the developing offspring depends on what type of gametes of the heterozygous sex are encountered during fertilization with a gamete of the homozygous sex. The same proposal was made by G. Mendel.
This proposal was confirmed at the beginning of the twentieth century, when T. Morgan and his colleagues were able to establish that males and females differ in the set of chromosomes. How?
- Independent practical work of students.Organized independent work with textbook materials to find an answer to the question posed.
Task 1. Fill out the diagram
Genetics of human sex
Task 2. Fill out the table
Taxonomic groups, organisms | Zygote type | Sex chromosomes |
||
Female body | Male body | eggs | spermatozoa |
|
Humans, mammals, reptiles, mollusks, Drosophila fly | XX | X Y | X and X | X and Y |
Birds, some fish, butterflies | X Y | XX | X and Y | X and X |
Orthoptera | XX | X O | X and X | X and O |
Mole | X O | XX | X and O | X and X |
The presence of sex chromosomes XX and XY not only explains the presence of male and female sexes, but also determines the birth of an equal number of children of both sexes.
However, contrary to theoretically expected equality, a strict 1:1 ratio is not observed among boys and girls born. Usually more boys are born than girls. For example, for every 100 girls among the white population, 106 boys are born. On average, there are 103 boys per 100 newborn girls, by adolescence there are 100 boys per 100 girls, by the age of 50 there are 85 men per 100 women, and by the age of 85 there are only 50 men per 100 women.
This so-called secondary change in sex ratio is explained by their different viability. In both humans and animals, the male sex turns out to be less resistant to unfavorable environmental factors, and the life expectancy of males is therefore shorter than that of females.
Speech by a student with the message “Determination of sex in humans” (presentation)
Determining sex in humans
At the end of the 40s, the scientist M. Barr discovered differences in the structure of the interphase nuclei of somatic cells in female and male cats: in the nuclei of the cells of females, a peculiar chromatin clump was discovered, called sex chromatin, or Barr's body. One X chromosome is always active and has a normal appearance. The other, if present, is in a resting state, in the form of this very Bara body. Therefore, the number of Bar bodies is always one less than the number of existing X chromosomes, i.e. in a male ( XY ) there are none, but the female ( XX ) - only one. This pattern turned out to be characteristic of mammals, including humans.
The presence of sex chromatin is easily determined by examining epithelial cells in a scraping of the buccal mucosa. The epithelial cells contained in the scraping are stained and examined under a microscope. Consequently, it is possible to distinguish male cells from female cells both directly, by analyzing the chromosome set of somatic cells, and indirectly, by the presence of sex chromatin.
Using this method, some gender anomalies are currently diagnosed, for example: Klinefelter syndrome (♂, XXY), Turner syndrome (♀ XO). (See presentation ).
Task 3. Solving problems.
1. In humans, the hemophilia gene is linked to the X chromosome. A girl whose father is a hemophiliac marries a healthy man. Determine the probability of having a sick child in a marriage.
2. In humans, the gene for color blindness is linked to the X chromosome. A colorblind son was born to a carrier mother and healthy father. What is the probability of having a sick child if this son starts a family with a carrier girl in the future?
3. The daughter of a colorblind person marries the son of another colorblind person, and the bride and groom distinguish colors normally. Build a pedigree for this family and determine what kind of vision the children will have? It is known that the color blindness gene is transmitted as a recessive trait linked to the X chromosome.
4. Hymenopacity is transmitted via the Y chromosome. Determine the possible phenotypes of children from the marriage of a webbed man and a normal woman.
5. The proband has teeth of normal color. His sister's teeth are brown. The proband's mother has brown teeth, while the father's teeth are of normal color. Seven sisters of the proband's mother have brown teeth, and four brothers have normal teeth. One proband's maternal aunt, who has brown teeth, is married to a man with normal teeth. They have three children: a daughter and son with brown teeth and a daughter with normal teeth. Two maternal uncles of the proband are married to women without anomalies in tooth coloring. One of them has two sons and a daughter, the other has two daughters and a son. All of them have normal teeth. The proband's maternal grandfather had brown teeth, and his maternal grandmother had normal teeth. Two brothers of the maternal grandfather with normal teeth coloring. The great-grandmother (maternal grandfather's mother) and great-great-grandmother (that great-grandmother's mother) had brown teeth, and their husbands had white teeth.
Construct a pedigree, determine the type of inheritance of the trait, the genotype of the proband and the probability of having children with an anomaly in the proband’s family, provided that he marries a woman heterozygous for this trait.
4. Checking diaries. The teacher checks the correctness of assignments
5. Summing up. Grading with teacher comments
6. Homework.
X-chromatin(Barr body) is a chromocenter about 1 μm in size, stained more intensely with all basic nuclear dyes than other chromatin structures of the nucleus. A Feulgen-positive reaction indicates a high concentration of DNA in it.
Localization of X-chromatin in the core is different. In most tissues, it is found on the inner surface of the nuclear envelope and can be triangular, plano-convex, trapezoidal, U-shaped, or dumbbell-shaped. Sometimes X-chromatin has the appearance of a thickening or tooth of the nuclear membrane, connected to the nucleolus by a thin chromatin thread. In fusiform and rod-shaped nuclei, X-chromatin is located at one of the poles of the nucleus.
Less commonly X-chromatin located on the nucleolus or in the nucleoplasm, with this localization it has a spherical shape and is difficult to distinguish from other chromocenters that have the same size, but are non-sex specific. Therefore, in order to diagnose the sex of cells, most researchers take into account chromocenters located only at the nuclear membrane.
X-chromatin position can change in the same cells depending on their functional state, as well as during ontogenesis.
X-chromatin found in cells of various tissues in many mammals; in rodents (hamsters, rats, mice, guinea pigs), the chromatin structures of nuclei are represented by a large number of chromocenters, making it difficult to detect X-chromatin. In humans, sex differences in the structure of nuclei have been established in almost all tissues and organs.
Origin of X-chromatin. During the cell cycle, chromosomes undergo regular transformations, which consist of spiralization and despiralization of chromosomes and their reproduction. In interphase, maximally despiralized chromosomes form a nucleus with relatively homogeneous contents. Reproduction (DNA synthesis) of chromosomes occurs only in a despiralized state during the S-interphase.
Spiraling chromosomes enter prophase of mitosis and reach the greatest spiralization in the metaphase of mitosis and meiosis. However, they have minimal specific activity. At the same time, it has been established that chromosomes are always unevenly spiraled along their length and are divided into heterochromatic and euchromatic regions. Morphologically, these areas differ in color intensity and structural organization.
Euchromatic regions in interphase the nucleus despiralize, while heterochromatic ones tend to remain in a spiralized compact state in the form of chromocenters with a high DNA content. The spiralization of heterochromatic regions is accompanied by an inactive state of the genes contained in them. This feature is also characteristic of some euchromatic regions with highly functionally differentiated genes. Being spiralized in the interphase nucleus stage, the euchromatic regions also become genetically inactive.
Heterochromatization- a universal mechanism of genetic inactivation of chromosomal regions, regardless of whether they belong to heterochromatic or euchromatic regions. Therefore, the chromocenters found in the interphase nucleus can be formed by both heterochromatin and euchromatin. One of these chromocenters is X-chromatin.
Also Barr and Bertram suggested a connection between the phenomenon of X-chromatin and X chromosomes. Since then, the X-chromosomal nature of X-chromatin has been confirmed and refined by the data of numerous researchers.
X-chromatin formed by one of the X chromosomes of a female cell, which is in a heterochromatized state. Being spiralized, this chromosome is genetically inactive. In different cells of the soma in females, according to the principle of chance, the X chromosome is formed by the X chromosome received either from the father or from the mother. Consequently, the cells of the female body are mosaic in the function of the X chromosome: in some the paternal chromosome is active, in others the maternal chromosome. The formation of sex chromatin in female cells is determined genetically.
This is confirmed by the fact that in the early period of human embryo development When sex cannot yet be determined by the appearance of the gonads, the egg membranes of the male embryo do not have X-chromatin, despite the influence of maternal hormones. In a female embryo, X-chromatin appears on the 16th day of development, when there are 2500-5000 cells in the embryo.