The formula of the karyotype of somatic cells of a woman. The concept of human karyotype - report. The concept of human karyotype
Each biological species has its own set of chromosomes; a person has forty-six.
The totality of all structural and quantitative features of the complete set of chromosomes characteristic of cells of a given type of living organisms is called karyotype.
The karyotype of the future organism is formed in the process of fusion of 2 germ cells - an egg and a sperm. In this case, chromosome sets are combined.
Fig. To compile a karyotype, dividing cells are distributed on a plate so that their chromosomes are clearly visible, and photographed (a). The homologous chromosomes in the photograph are then paired and arranged in size so that they are much easier to study.
The nucleus of a mature cell contains half of the set of chromosomes - 23 - a single set of chromosomes is called haploid; when fertilized into the body, a karyotype specific to this species is recreated. The complete set of chromosomes (46) of an ordinary somatic cell is diploid (2p)
Human chromosomes, like many animals, can be divided into pairs. Forty-six human chromosomes form 23 pairs (Fig. 5.36). Arranging them in the photo in order, we get a karyotype, that is, a set of chromosomes with which you can diagnose some genetic diseases.
Two identical chromosomes are called homologous (they are not only similar in appearance, but also contain genes responsible for the same traits).
If we arrange them in order, starting with the longest, then we will come to the shortest pair, on which the difference between men and women depends.
Women have exactly 23 pairs of chromosomes, but in men the last two chromosomes remain unpaired, and one of them is extremely short.
This short chromosome is called Y-chromosome, and the longer one X chromosome.
In women, the 23rd pair contains two X chromosomes.
It is clear that the X and Y chromosomes determine the sex of a person (sex). The remaining 22 pairs of homologous chromosomes are called autosomes.
Obviously, each person has two identical chromosomes, because everyone has two parents.
The development of the human body begins with the fertilization of an egg by a spermatozoon; each gamete contains 23 chromosomes, one of each type, and the resulting zygote already contains two chromosomes of each type.
All autosomes are divided into 7 groups: A (1,2,3), B (4,5), C (6-12), D (13-15), E (16-18), F (19-20) , G (21-22).
The hereditary information of an organism is strictly ordered according to individual chromosomes. A cryotype is a species passport. The human karyotype is represented by 24 chromosomes, 22 autosomes, x and y chromosomes.
Karyotype analysis reveals disorders that can lead to developmental anomalies, hereditary diseases or fetal and embryonic death early stages development. Those. for normal development, a set of genes of a complete chromosome set is required.
Mitosis, its essence. Pathology of mitosis
The behavior of chromosomes during mitosis ensures a strictly equal distribution of hereditary material between daughter and mother cells.
Mitosis is a continuous process with 4 stages:
Prophase- chromatin threads begin to twist, spiralize. Chromosomes shorten and thicken, becoming available for microscopy. The nucleolus disappears, the nuclear envelope disintegrates. Centrisome divides into 2 centrioles, which move to different poles of the cell. From protein t ubulina microtubules are formed - threads of the achromatin spindle. Chromosomes are concentrated in the center.
metaphase- Chromosomes max are spiralized and located in the plane of the equator of the cell - it is convenient to view in a light microscope. Spindle threads from different poles are attached to the centromeres of all chromosomes.
Anaphase- characterized by the division of chromosomes in the centromere region into 2 chromatids. The spindle fibers contract and pull the chromatids of each chromosome to different poles of the cell. The shortest phase of mitosis.
Telophase- despiralization of chromosomes, turning them back into thin filaments of chromatin, invisible in a light microscope. Around each group of daughter cells, a nuclear envelope is formed, nucleoli appear. The fission spindle filaments disintegrate
The division of the cytoplasm in animal cells is preceded by the appearance of a CMP constriction.
Mitosis ends with the formation of 2 cells quantitatively and qualitatively identical to the mother cell.
Doubling of chromosomes and in the interphase of mitosis, uniform distribution of chromatids between daughter cells and cells ensures the maintenance of the constancy of genetic information in a number of generations of cells, serves as the basis for the growth and development of the organism.
Pathology of mitosis
Various factors external environment can disrupt the process of mitosis and lead to the appearance of abnormal cells.
There are 3 types of violations:
Change in the structure of chromosomes –
A) the appearance of chromosome breaks, the presence of small chromosomal fragments. Occurs under the influence of radiation, chemicals, viruses, as well as in cancer cells (mutations).
B) chromosomes can lag behind others in anaphase and not get into their cell. This will lead to a change in the number of chromosomes in daughter cells - aneuploidy.
Spindle damage- the function of distribution of chromosomes between daughter cells is disturbed - the appearance of cells containing a significant excess of chromosomes (for example, 92) is possible. A similar action is typical for anticancer drugs - this is how the growth of tumor cells is inhibited.
Violation of cytotomy– i.e. the absence of division of the cytoplasm of the cell during the telophase period. This is how binucleated cells are formed
The pathology of mitosis can lead to the appearance mosaicism- in one organism, clones of cells with a different set of chromosomes can be found (for example, some cells contain 46 chromosomes, and others - 47).
Mosaicism is formed in the early stages of cleavage of germ cells.
As a rule, karyotype disorders in humans are accompanied by multiple malformations; most of these anomalies are incompatible with life and lead to spontaneous abortions in the early stages of pregnancy.
However, a fairly large number of fetuses (~2.5%) with abnormal karyotypes endure before the end of pregnancy.
Meiosis
A type of division in which the number of chromosomes is reduced by half from diploid to haploid, consisting of 2 consecutive divisions of the nucleus.
called meiosis. With each fertilization, the original number of chromosomes is restored.
Sexual reproduction can thus be thought of as the following great cycle of events:
In the sex glands (gonads) of an adult organism - the testes and ovaries - some cells multiply through meiosis, forming respectively spermatozoa and eggs, that is, haploid cells. These gametes each contain one set of 23 chromosomes. During fertilization, a zygote with a double set of chromosomes is formed; and during mitotic division, an adult organism grows out of it, and the cycle begins anew.
The division mechanism - the formation of a centriole, spindle, etc. - is the same during meiosis as during mitosis, only the chromosomes behave somewhat differently.
Meiosis
Rice. 5.4. meiosis process(V in general terms) in a cell with two pairs of chromosomes; one of the paired chromosomes is indicated by a thick line, the other by a dotted line.
Prophase I: Chromosomes become visible and form pairs.
Metaphase I: paired chromosomes line up opposite each other in the middle of the cell.
Anaphase I: each of the paired homologous chromosomes completely departs to one of the poles of the cell. Note that the chromatids do not separate and are still connected by centromeres.
Telophase I: The initial division is completed.
Prophase II: Chromosomes become visible again, as in mitotic division.
Metaphase II: Chromosomes line up again in the middle of the cell.
Anaphase II: This time the chromatids separate from each other and diverge towards opposite poles.
Telophase II: division ends with the formation of four haploid cells
The biological significance of meiosis:
Sexual reproduction - this process ensures the constancy of the number of chromosomes in a number of generations of sexually reproducing organisms.
Genetic variability - creates the possibility for new gene combinations. This leads to changes in the genotype and phenotype of the offspring.
Pathology of meiosis: under the influence of external damaging factors: simple, sequential and double nondisjunction.
Simple nondisjunction:
With the pathology of meiosis 1, all mature gametes will have a pathological set of chromosomes
Meiosis 2 - the number of chromosomes changes only in part of the gametes.
Sequential nondisjunction - affects both divisions 1 and 2, normal gametes are not formed.
Double nondisjunction- extremely rare - meiosis is damaged in both parents.
It is also possible to distinguish primary, secondary and tertiary nondisjunction of chromosomes.
The process of meiosis can be disturbed under the influence of various external adverse factors.
Balanced changes in chromosomes in the human karyotype do not affect the state of human health.
Chromosomes (from the Greek Chromoc - painted, soma - body) - the structures of the nucleus, which are the material carriers of hereditary information. These nuclear organelles are formed as a result of compaction and spiralization of chromatin and become visible during cell division. At the metaphase stage, the chromosomes line up at the equator of the cell, forming metaphase plate. Chromosomes consist of DNA, RNA, nuclear proteins and enzymes necessary for their duplication or mRNA synthesis.
Quantity chromosomes in the cells of organisms different types is different and does not depend on the height of the organization, and also does not always indicate a phylogenetic relationship.
The number of chromosomes in some species
Structure . In the structure of the metaphase chromosome, chromatids, primary constriction, shoulders, secondary constriction, satellites, nucleolar organizers, telomeres, etc. are distinguished. Each such chromosome consists of two longitudinal parts - chromatids. Primary constriction(centromere) - the most spiralized part of the chromosome, divides it into two shoulder. Special proteins (kinetochore) are located on it, to which, during the distribution of genetic material, the fission spindle threads are attached. Some chromosomes have secondary straps, often separate segments of chromosomes called satellites. Such chromosomes in the nuclei of cells can approach each other and form nucleolar organizers, containing rRNA genes. The ends of the shoulders are called telomeres. These are genetically inactive spiralization regions that prevent the connection of chromosomes with each other or with their fragments.
Varieties . Chromosomes differ in size, shape, arrangement of constrictions, degree of spiralization, and the like. Chromosomes can be grouped in pairs based on size and shape, and these paired chromosomes are called go-
1- centromeric region of the chromosome; 2 - telomeric region; 3 - daughter chromatids; 4 - heterochromatin; 5-euchromatin; 6 - small shoulder, 7 - large shoulder.
molologic, and the chromosomes of different pairs will be relative to each other non-homological. The arrangement of the constrictions also allows the division of chromosomes into groups. If the constriction is located in the middle, and the arms are of the same size, then the chromosomes are called equal-arm, if the dimensions of the arms are significantly different, they are uneven-arm. Chromosomes can be in two states: in a helix; mitosis chromosome) and despiralized ( interphase chromosome). When comparing the chromosome sets of male and female individuals of the same species, a difference is observed in one pair of chromosomes. This couple is called sex chromosomes, or heterochromosomes. The remaining pairs of homologous chromosomes, which are the same in both sexes, have common name autosomes. To elucidate the functioning of the hereditary apparatus, it is necessary to study chromosomes not only during mitosis, but also at the stage of interphase. In some insects and other organisms, the interphase chromosomes are much thicker and can be clearly seen under a light microscope. Polytennichromosomes - chromosomes, which are a bundle of numerous (more than 1000) chromatids stretched in length. These chromosomes are formed as a result of multiple replication and non-disjunction of daughter chromosomes. During the experiment on special coloring, alternation of light (decondensation area) and dark (condensed areas) bands was found in them. The number, size, and arrangement of these bands are species-specific. There are polytene chromosomes in some insects, in the endosperm of seeds, in the embryonic tissues of plants, and the like. They study polytene chromosomes for: a) clarification of the work of genes that are needed in this moment cell (light unfolded DNA bands - puffs - available for transcription) b) building genetic maps; c) detection of chromosomal rearrangements; d) identification of the species belonging of organisms, etc.
Organization . Chromosomes have several levels of organization.
1. Organization of chromonemes. DNA molecules at this level of chromosome organization spirally braid from the outside special nuclear particles from histone molecules, which are called nucleosomes. Each nucleosome contains 8 protein molecules. The strands of nucleosomes with DNA twist in pairs, forming chromonemes (DNA + nucleosomes = chromonemes).
2. Organization of chromatids. Chromonemes spiralize to form compact chromatids.
3. Organization of chromosomes. Chromatids after self-duplication and supercoiling form two-chromatid chromosomes.
biological significance Chromosomes are determined by such functions as: a) the preservation of hereditary information; b) control of metabolism by regulating the formation of necessary enzymes; c) ensuring cell growth by controlling the synthesis of structural proteins; d) ensuring the development of cells by controlling the processes of differentiation; e) providing conditions for DNA duplication and cell division.
The concept of karyotype
Karyotype - a set of features of the chromosome set (number of chromosomes, shape, size). Each type of organism has a specific karyotype. The main rules characterizing the karyotype are:
specificity rule - features of the karyotype of individuals of a particular species depend on the number, size and shape of chromosomes;
stability rule - each type of eukaryotic organisms has a certain and constant number of chromosomes (for example, in Drosophila - 8 chromosomes, in humans - 46);
pairing rule- in the diploid set, each chromosome has a pair, similar in size and shape;
rule of individuality each pair of homologous chromosomes is characterized by its own characteristics;
rule of succession (continuity) - due to the ability of chromosomes to self-reproduce during cell division, in the next generations of cells of the same species, not only a constant number of chromosomes is preserved, but also their individual characteristics.
The chromosome set is diploid, haploid, polyploid.
■ haploid set - this is a half set in which all chromosomes differ from each other in structure (it is conventionally designated 1p).
■ Diploid set - this is a paired set in which each chromosome has a paired chromosome similar in structure and size (it is conventionally designated 2p).
■ Polyploid set - this is a set of chromosomes that is a multiple of the haploid one (it is conventionally designated 3p, 4p, 5p, etc.).
BIOLOGY + American scientists Elizabeth Blackburn, Carol Greider and Jack Szostak figured out which chip the chromosomes maintain their integrity during cell division. They found that the reason for this is at the ends of chromosomes, known as telomeres. (their enzyme - telomerase) . These scientists hypothesized that cancer cells use the enzyme telomerase to ensure their uncontrolled division. In addition, the gradual reduction in telomere size with age is considered one of the main mechanisms of aging. Telomere defects are also the cause of several hereditary diseases of the skin and lungs. For these studies, these scientists became the owners of Nobel Prize 2009 in Medicine and Physiology.
Omnis cellula e cellula
latin proverb
The concept of human karyotype.
The number, size and shape of chromosomes are specific features for each type of living organisms. So, hermit crab cells contain 254 chromosomes, while mosquitoes have only 6. Human somatic cells contain 46 chromosomes.
The totality of all structural and quantitative features of the complete set of chromosomes characteristic of cells of a particular type of living organisms is called karyotype.
The karyotype of the future organism is formed in the process of fusion of two germ cells (sperm and egg). At the same time, their chromosome sets are combined. The nucleus of a mature germ cell contains a half set of chromosomes (for humans - 23). A similar single set of chromosomes, similar to that in germ cells, is called haploid and is marked - n. When an egg is fertilized by a sperm in a new organism, a karyotype specific for this species is recreated, which includes 46 chromosomes in humans. The complete composition of the chromosomes of an ordinary somatic cell is diploid (2n) .
In a diploid set, each chromosome has another paired chromosome similar in size and location of the centromere. Such chromosomes are called homologous. Homologous chromosomes are not only similar to each other, but also contain genes responsible for the same traits.
When analyzing somatic cells female body Normally, 23 pairs of homologous chromosomes can be clearly distinguished. At the same time, in the karyotype of a man, one pair of chromosomes is found, which differ from each other in size and shape. One of them is a rather large submetacentric chromosome, which was designated X, the other is a small acrocentric, Y. It was proved that these chromosomes determine the sex of the organism and contain most of the genes responsible for the formation of the genitals, so they were called sex chromosomes.
The karyotype of a woman normally contains two X chromosomes, and it can be written - 46, XX.
The male karyotype includes X and Y chromosomes (46, XY).
All other 22 pairs of chromosomes are named autosomes. Each pair of autosomes, in descending order of their size, is assigned a number from 1 to 22. The longest are the chromosomes of the 1st pair, and the shortest are the 21st.
In 1960, in Denver (USA), the first classification of human chromosomes was adopted, which took into account their size and location of the centromere. The universal system for recording the results of chromosome analysis unified the clinical assessment of the human karyotype, regardless of the cytogenetic laboratory in which the study was carried out. Since 1995, the International System for Human Cytogenetic Nomenclature or ISCN (1995) has been used all over the world, which is based on the latest achievements in molecular genetic diagnostics.
All autosomes divided into 7 groups, which are designated in Latin letters. Group A includes 3 pairs of the longest chromosomes (1, 2, 3rd); group B combines 2 pairs of large submetacentric chromosomes (4 and
5th). The most numerous is group C, which includes 7 pairs of medium submetacentric autosomes (from the 6th to the 12th). According to morphological features, the X chromosome is difficult to distinguish from this group. Medium acrocentric chromosomes of the 13th, 14th and 15th pairs are included in group D. Three pairs of small submetacentric chromosomes make up group E (16th, 17th and 18th). The smallest metacentric chromosomes (19 and 20) make up group F. The 21st and 22nd pairs of short acrocentric chromosomes are included in group G. The Y chromosome is morphologically very similar to the autosomes of this group.
Human karyogram analysis1. The concept of karyotype and karyogram.
Karyotype- this is the totality of all chromosomes of the diploid set of the cell, which is characterized by the number of chromosomes and structural features of each chromosome. The normal karyotype is characterized by the following:
there is a normal number of chromosomes,
all chromosomes are represented by pairs of chromosomes homologous to each other,
each chromosome has a normal structure: its characteristic location of the centromere, the ratio and structure of the arms, there are no chromosomal mutations.
Organisms of different species differ in karyotype: in the number and / or individual characteristics of certain chromosomes. The human karyotype and chromosomes have many features common to the karyotype and chromosomes of organisms of other species.
Chromosomes are made up of chromatin, a complex of DNA with numerous proteins.
The structural unit of chromatin is the nucleosome - a complex of four pairs of histone proteins, around which about two turns of the DNA molecule are wound. There is only one DNA molecule per chromosome, which is wound around thousands of histone complexes.
different plots Chromatins differ in the degree of condensation, or packing in space. Euchromatin is weakly condensed and contains actively functioning genes. Heterochromatin is highly condensed and contains non-functioning genes and sections of DNA that do not contain genes. Heterochromatin regions are stained with dyes more strongly than euchromatin regions and look darker under a microscope.
During cell division, chromatin, condensing, takes the form of dense rod-shaped structures, which are especially clearly visible in the metaphase of mitosis.
A diploid set of chromosomes is a set of pairs of homologous chromosomes. The chromosomes of each pair are homologous to each other and non-homologous to all other chromosomes. The human karyotype includes 46 chromosomes: 22 pairs of autosomes and two sex chromosomes: two X chromosomes in women, X and Y chromosomes in men.
Non-homologous chromosomes differ in length and shape, have approximately the same thickness.
All chromosomes have two arms and a thin section located between them - the centromere, or primary constriction. In the region of the primary constriction, there is a kinetochore - a flat structure, the proteins of which, interacting with microtubules of the division spindle, ensure the movement of chromosomes during cell division.
Some chromosomes have a secondary constriction, in the region of which the ribosomal RNA genes are located, rRNA synthesis occurs and the nuclear nucleolus is formed. In humans, chromosomes 13, 14, 15, 21, and 22 have a secondary constriction.
The karyotype contains three types of chromosomes, differing in the location of the centromere and, accordingly, the ratio of the arms.
The ends of each chromosome are telomeres. In humans, the DNA of the telomeric region is a repeatedly repeated nucleotide sequence 5 "TTAGGG 3" in one of the DNA nucleotide chains.
After each act of replication and cell division, the telomeric regions of chromosomes are shortened.
The diploid set of females has two X chromosomes, while the diploid set of males has one X chromosome and one Y chromosome. X and Y chromosomes differ in length, shape, and sets of genes. In humans, the SRY gene on the Y chromosome determines male development.
During prophase and metaphase of mitosis, each chromosome consists of two identical chromatids - identical copies of the maternal chromosome formed after DNA replication.
^ 2. Obtaining a karyogram.
To study the karyotype, peripheral blood leukocytes, red bone marrow cells and some other cells are usually used. If necessary, the cells of the membranes of the embryo and fetus are studied, since they have the same karyotype and genotype as the cells of an unborn organism, since they are also descendants of the zygote.
Cells interfere with nutrient medium and encourage them to divide with the help of special division stimulants. Phytohemagglutinin (PHA) is one of the division stimulators. Phytohemagglutinin is a carbohydrate of the common bean Phaseolus vulgaris, capable of agglutinating erythrocytes. Phytohemagglutinin is a strong mitogen - a substance that stimulates cell division by mitosis.
Under the influence of PHA, cells begin to divide by mitosis. Colchicine is then added to the culture medium with dividing cells. It is an alkaloid of plant origin, usually obtained from autumn colchicum (winterer) ( Colchicum autumnale) or other members of the lily family. Colchicine prevents the formation of microtubules from tubulin protein. In a dividing cell, microtubules are part of the division spindle and normally first ensure the movement of all chromosomes to the equator region of the division spindle, and then participate in the divergence of the chromatids of each chromosome in different directions, to different poles of the cell division spindle. Therefore, in the presence of colchicine, the division of all cells stops at the same stage of mitosis: at the end of prophase, immediately before metaphase. In foreign scientific literature this stage is called prometaphase. At this stage, all chromosomes are completely condensed and are clearly visible in a light microscope in the form of rod-shaped structures located in the same plane. The totality of all such chromosomes of one cell is called metaphase plate(Fig. 1).
For ease of study, living cells are placed in a hypotonic solution. table salt. In such a solution, water enters the cell, the cell increases in size, and the chromosomes are more freely distributed in the cytoplasm - at a greater distance from each other than before.
The chromosomes are then stained, photographed and examined under a microscope. Staining is carried out with simple, differential or fluorescent dyes that help identify chromosomes.
Fig.1. Human metaphase plate.
1 - large metacentric chromosome
2 - small acrocentric chromosome
3 - large submetacentric chromosome
4 - small metacentric chromosome
5 - middle acrocentric chromosome.
As can be seen from Fig. 1, chromosomes differ in size and shape. All of them have X- or Y-shape, which is due to the fact that the daughter chromatids - copies of the maternal chromosome - remain connected in the region of the primary constriction.
In the metaphase plate, each chromosome consists of two identical chromatids. For each chromosome of the diploid set, there is only one chromosome paired with it. Paired chromosomes are called homologous chromosomes. Homologous chromosomes have the same external signs: length; the shape (location of the primary constriction and the correspondence of the shoulders, the presence or absence of a secondary constriction) and the same degree of chromatin condensation in certain areas: areas with strongly condensed chromatin look dark, and areas with weakly condensed chromatin appear lighter. According to the same features, non-homologous chromosomes differ from each other. Distinguish the following types human chromosomes (Fig. 2):
Metacentric, equal-arm chromosomes: the primary constriction (centromere) is located in the center (in the middle) of the chromosome, the chromosome arms are the same.
Submetacentric, almost equal-arm chromosomes: the centromere is located not far from the middle of the chromosome, the arms of the chromosome differ slightly in length.
Acrocentric, very unequal chromosomes: the centromere is very far from the center (middle) of the chromosome, the chromosome arms differ significantly in length.
Fig.2. Types of human chromosomes.
Since each pair of chromosomes homologous to each other has characteristics characteristic of them, this makes it possible to identify specific chromosomes. Having identified the chromosomes, they build a karyogram: they arrange the chromosomes in order of decreasing size, decomposing them into groups depending on size and shape. When constructing a karyogram, sex chromosomes are located separately from autosomes, although the X chromosome belongs to group C chromosomes, and the Y chromosome belongs to group G chromosomes.
A karyogram is built when studying the karyotype of a particular person. A generalized, idealized karyogram, in which the features of the karyotype of a species are presented, is called idiogram. When identifying chromosomes and constructing a karyogram of a specific person, a geneticist always has a sample in front of him - an idiogram of the species Homo sapiens.
On fig. Figure 3 shows a karyogram of a man with a normal karyotype. The box shows the sex chromosomes of a woman with a normal karyotype.
Rice. 3. Normal karyogram of a person.
In the first seven rows of the karyogram, autosomes of groups A - G are presented. They are the same in the karyotypes of male and female organisms. The last row shows the sex chromosomes. In the male karyotype, this is the X chromosome of group C and the Y chromosome of group G. In the female karyotype, these are two X chromosomes. Thus, the karyograms of the male and female organisms are easy to distinguish from each other: the karyogram of the female body contains two identical metacentric chromosomes of medium size - X-chromosomes, and the karyogram of the male body contains two chromosomes that are different in size and shape: one metacentric chromosome of medium size - X- chromosome and one small acrocentric chromosome - the Y chromosome.
The procedure for compiling a karyogram manually is laborious and requires a certain sequence of actions. Drawing up a karyogram is part of the laboratory work performed by first-year students of the Medical University.
IN last years to identify chromosomes and build a karyogram using computer programs. In this case, the image of the metaphase plate enters the computer through a video camera connected to a fluorescent microscope.
^ 3. Laboratory work "Compilation of a karyogram of a person."
On laboratory work each student receives an envelope with a set of 45-47 images of human chromosomes and a sheet of paper with the names of groups of chromosomes. The task of the student is the correct decomposition of chromosomes into groups.
All chromosomes, depending on the shape, divide into two large groups:
acrocentric chromosomes
metacentric and submetacentric chromosomes
Notice the acrocentric chromosomes. Divide all acrocentric chromosomes into two small groups depending on size:
medium acrocentric chromosomes.
small acrocentric chromosomes
Small acrocentric chromosomes are group G chromosomes. In a normal karyotype, there may be 4-5 chromosomes, depending on the sex of the person. In a normal female karyotype, these are 2 pairs of autosomes, in a normal male karyotype, 2 pairs of autosomes and one Y chromosome. In people with s. Downa and s. extra Y-chromosome group G can contain 5-6 chromosomes. Unfortunately, conventional staining of chromosomes does not allow us to distinguish between chromosome 21 and the Y chromosome with certainty. For this reason, the set of images of 5 chromosomes of group G may also belong to a woman with s. Down, and a man from s. Klinefelter, and the set of images of 6 chromosomes of the G group can belong to both a man with s.Down and a man with an additional Y-chromosome in the karyotype. If you have only 2 pairs of chromosomes of this group, then put their images on a sheet with the names of groups of chromosomes opposite the name of group G. If you have two more chromosomes of this group, then put one of them next to the chromosomes of the 21st pair, and the other - in place of the sex chromosomes, considering it a Y-chromosome. If you have 5 chromosomes of this group, then until the end of the karyogram, you can consider it a chromosome of the 21st pair or a Y-chromosome. Depending on your preliminary choice, put the 5th chromosome of this group in the appropriate place on the sheet with the names of the groups of chromosomes.
Medium acrocentric chromosomes are chromosomes of group D. There are 3 pairs of them in a normal karyotype. With s. Patau in the human karyotype, 7 chromosomes of this group are found due to the additional chromosome of the 13th pair. Put the images of group D chromosomes on the sheet with the names of groups of chromosomes in the appropriate place.
You have decomposed all the acrocentric chromosomes. Now pay attention to the remaining undecomposed metacentric and submetacentric chromosomes. All these chromosomes, depending on the size, are divided into two small groups:
large and medium chromosomes
short and small chromosomes.
Pay attention to the short and small chromosomes of the last group. Choose from them 2 pairs of the smallest metacentric chromosomes. These are chromosomes of group F. Put the images of chromosomes of this group on the sheet with the names of groups of chromosomes in the appropriate place. The remaining chromosomes are the chromosomes of the E group. There are 3 pairs of them in a normal karyotype. With s. Edwards in the human karyotype, 7 chromosomes of this group are found due to the additional chromosome 18 pair. Put the images of the chromosomes of this group on the sheet with the names of the groups of chromosomes in the appropriate place.
Pay attention to the large and medium chromosomes that have not been decomposed. Choose from them 3 pairs of the largest chromosomes. These are the metacentric chromosomes of group A. Put their images on a sheet with the names of chromosome groups.
From the remaining chromosomes, select the 2 pairs of the largest chromosomes. These are the metacentric chromosomes of group B. Put their images on the sheet with the names of the groups of chromosomes in the appropriate place.
All remaining chromosomes are submetacentric chromosomes of group C. 7 pairs of chromosomes of this group are autosomes. Put their images on a sheet with the names of groups of chromosomes opposite the name of group C. All other chromosomes of this group are X chromosomes. The number of X chromosomes in the karyotype of a particular person can be 1-3. Put the images of the X chromosomes on the sheet with the names of the groups of chromosomes in the appropriate place.
Carefully study the karyogram you have compiled. The karyogram should not contain two major anomalies at the same time, since this does not occur in real life. This can happen if you misidentified the Y chromosome as chromosome 21. For example, a karyogram cannot contain both trisomy on the 21st chromosome and monosomy on the X chromosome, that is, a karyogram cannot belong to a person suffering simultaneously with. Down and S. Shereshevsky-Turner. Most likely, you have a normal karyogram of a man at your disposal. To correct the error, it is enough to transfer one of the 3 chromosomes of the 21st pair to the location of the sex chromosomes, placing it next to the X chromosome. When compiling a karyogram for a specific person, this situation does not arise, since even before the start of compiling a karyogram, the gender of the person and the preliminary diagnosis are known.
^ 3. Analysis of human karyogram.
When analyzing a karyogram, the student is required to:
be able to identify the gender of a person
be able to identify a normal human karyotype
be able to identify the presence of a chromosomal disease associated with an anomaly in the number of chromosomes (p. Down, p. Klinefelter, p. Shereshevsky-Turner, p. Trisomy - X, p. Patau, p. Edwards, p. extra Y-chromosome).
total chromosomes;
pairing or unpairedness of certain chromosomes;
number and type of sex chromosomes;
the presence of certain anomalies in the number of chromosomes.
Number the pairs of homologous chromosomes; number them even if the homologous chromosomes are represented not by two, but by one or three chromosomes.
Locate the autosomes and sex chromosomes on the karyogram. The sex chromosomes are usually located separately from the autosomes. A normal karyogram contains 22 pairs of autosomes and 1 pair of sex chromosomes. The karyogram of a sick person may contain 45-46 autosomes and 1-3 sex chromosomes.
Determine the gender of a person by his karyogram. To do this, carefully study the sex chromosomes.
If they are all the same, medium in size and metacentric, then they are all X chromosomes, and in front of you is a karyogram of a female body.
If there is a small acrocentric chromosome among the sex chromosomes, then this is a Y-chromosome, and in front of you is a karyogram of the male body.
See if all chromosomes are in pairs.
If the karyogram contains 23 pairs of chromosomes, then you have a normal human karyogram.
If certain chromosomes are represented in the karyogram by 1 or 3 chromosomes, then you have a karyogram with a genomic mutation - the absence or excess of chromosomes. In this case, the karyogram contains 45 or 47 chromosomes.
Determine the serial number of the pair of chromosomes in which the genomic mutation is found. The most common anomalies are:
anomalies in the number of autosomes:
Additional chromosome of the 18th pair at s. Edwards
Additional chromosome of the 21st pair at s. Down
anomalies in the number of sex chromosomes:
Additional X-chromosome in the male karyogram with s. Klinefelter
Additional Y-chromosome in the male karyotype in c. extra Y chromosome
Lack of X-xpromosomes in the female karyotype in s. Shereshevsky-Turner.
The analysis of the karyogram ends with the recording of the karyotype formula. The karyotype formula includes the following:
b) recording a combination of sex chromosomes,
C) information about the anomaly in the number of chromosomes (if any): indicate the chromosome and type of anomaly. For example:
The formula of the karyotype of a woman suffering from Down syndrome: 47, XX, 21+;
The karyotype formula of a man suffering from Klinefelter's syndrome: 47, XXY,
Karyotype formula of a woman with Shereshevsky-Turner syndrome: 45, X0.
^ 4. Example of human karyogram analysis.
Exercise. Make an analysis of the human karyogram (Fig. 4).
Rice. 4. Kariogram of a person.
A human karyogram contains 47 chromosomes. Most chromosomes are arranged in order of decreasing size. These are autosomes. In the bottom row, away from them, there are three chromosomes. These are the sex chromosomes. All autosomes are presented in pairs. In total, there are 22 pairs of autosomes in the karyogram. There are 3 sex chromosomes. Two of them are large and their primary constriction - the centromere - is located almost in the middle. These are X chromosomes. Next to them is a small chromosome with a primary constriction located closer to the edge of the chromosome. This is the Y chromosome. The karyogram belongs to the male, since there is a Y-chromosome. The karyogram contains an anomaly: an extra X chromosome. Such a karyogram is typical for males suffering from Klinefelter's syndrome: patients have a eunuchoid physique, sometimes enlarged mammary glands, weak facial hair, often mental retardation, infantilism, they are barren. Human karyotype formula - 47, XXY.
^ 5. Task for independent work.
Analyze the following karyograms.
Kariogram 1.
Kariogram 2.
Kariogram 3.
Kariogram 4.
^ 6. Improvement in the study of human karyogram.
6.1. Differential staining of chromosomes
Modern cytogenetic techniques make it possible to identify all pairs of chromosomes on the preparation by morphology. The essence of these methods is differential staining of chromosomes along the length, which is provided by relatively simple temperature-salt effects on fixed chromosomes or the use of specific dyes. Differential staining results in a linear pattern along the length of the chromosome.
Despite the wide variety of methods of processing chromosome preparations and dyes, the revealed linear pattern of the chromosome is always the same. It changes only depending on the degree of condensed state of the chromosome. A segment seen as a single band on a metaphase chromosome may appear as several small bands on a less condensed prometaphase chromosome.
Differential staining, depending on the method used, can cover either the entire length of the chromosome or its centromeric region.
An idea of the pattern of chromosomes that are differentially stained along the entire length can be obtained by staining preparations by the G-method using Giemsa stain (Fig. 5). In this case, the chromosomes appear to consist of cross-striated, differently colored segments. Each pair of chromosomes has an individual pattern of striation due to the unequal size of the segments. In small chromosomes, the pattern is formed by single segments, in large chromosomes there are many segments. The total number of stained and unstained segments in metaphase for a normal chromosome set is about 400. In prometaphase chromosomes, it increases to 850 or more.
Rice. 5. Schematic representation chromosomes person at G-staining in accordance with international classification
^ 6.2. Method of fluorescent hybridization in situ.
Advances in human molecular cytogenetics have made it possible to develop new methods for studying chromosomes. One of them is the method of fluorescence in situ hybridization (FISH). This method is based on the complementary interaction of the DNA of the object under study with a small artificial DNA nucleotide sequence, called a DNA probe. The DNA probe is connected to a fluorescent substance. The complementary interaction of the DNA of the studied object and the DNA probe is called DNA hybridization. If hybridization occurs, then this event is recorded by a luminescent microscope and indicates the presence in the test sample of a DNA fragment complementary to the DNA probe. Using this method, having a set of different DNA probes, even in a nondividing cell, it is possible to detect an anomaly in the number of chromosomes and the presence of a pathological gene, as well as to detect small chromosomal mutations that are difficult to detect using conventional methods. At the same time, different chromosomes or their parts look like multi-colored structures (Fig. 6, 7).
Rice. 6. Normal female human karyogram obtained using the spectral karyotyping technique.
Rice. 7. Kariogram of a man with the transfer of a segment of the 1st chromosome to the 3rd and the loss of a segment of the 9th chromosome.
Biologists have long associated genetic phenomena that characterize heredity and biological variability with special nuclear formations - chromosomes, which with good reason are considered as structures in which genes are located. In the history of genetics as a science, for a long time, in the absence of real knowledge about the material carrier of the properties of heredity and variability, and thanks to the advanced development of microscopic technology, chromosomes were in fact the only object for direct observation. This led to the emergence of the cytogenetic method of genetic analysis, which still holds an important place, as well as a special concept - karyotype.
Karyotype- this is a diploid set of chromosomes (2n), characteristic of the somatic cells of organisms of a given species, which is a species-specific complex trait and is characterized by a certain number, structure and gene composition of chromosomes.
Karyotypes of organisms various kinds: I - skerda; II - Drosophila; III - man
If the number of chromosomes in a single haploid set of chromosomes of germ cells is denoted by n, then the karyotype formula will look like 2n. The value of n usually varies between species. Thus, the haploid number of chromosomes in human gametes is 23 (n = 23), and the diploid number corresponding to the karyotype is 46 (2n = 46).
Each chromosome is represented in a karyotype pair of homologues. One of the homologous chromosomes of the pair is inherited from the father, the other - from the mother through the germ cells of the parents who took part in fertilization. Gene composition pairs of homologous chromosomes are the same. At the same time, the same gene in homologues can be represented by its different alternative forms or alleles (allelic genes). Given the known relationships between alleles in dominance and recessive, as well as the presence in homologous chromosomes of the same, or dominant, or recessive alleles, or different alleles (dominant and recessive), the following conditions are possible:
- dominant homozygosity,
- recessive homozygosity,
- heterozygosity.
In karyotypes strictly homologous chromosomes (autosomes) all pairs are represented, except for one (heterochromosomes or sex chromosomes). In cells, a pair of sex chromosomes in individuals of one sex (homogametic sex, in humans - female) is represented by two identical chromosomes (in humans - XX), while in the other (heterogametic sex, in humans - male) two different chromosomes(in humans - XY). In the first case, the gene composition of a pair of sex chromosomes is the same. Therefore, depending on the match or mismatch in the two chromosomes X alleles of the corresponding genes are reproduced known states dominant or recessive homozygosity and heterozygosity. Most of the genes of different sex chromosomes of individuals of the heterogametic sex are different. As a result, it is possible hemizygosity, when in individuals of the heterogametic sex (in humans, male - XY), the gene of the X chromosome, without a homologue on the Y chromosome, is present in the karyotype in a single copy. Such a gene will definitely manifest itself in the phenotype, even if it is represented by a recessive allele. There are species in which females and males differ in the number of heterochromosomes, respectively. XX and HO.
Karyotype rules :
- constancy,
- pairing,
- personality,
- continuity.
The number of chromosomes in cells of a certain type is always the same. The number of chromosomes - specific sign . This feature is known as constancy rule number of chromosomes . In the somatic cells of representatives of any biological species, the number of chromosomes is even, according to how many chromosomes make up pairs. Paired chromosomes are called homologous. They coincide in size, shape, other details of the structure, the order of the hereditary material. This rule is true for all autosomes and heterosomes of the homogametic sex. The sex chromosomes of the heterogametic sex do not match in all details of the structure and set of genes. Non-homologous chromosomes always have morphological and functional differences.
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