Chromosomes

Chromosomes are the basic structural elements of cell nucleus that carry genes that coded hereditary information. Having the ability to reproduce, chromosomes provide genetic link between generations.
Morphology of chromosomes linked to the degree of their circling. For example, if the stage of interphase (see Mitosis, Meiosis) chromosome maximum deployed, i.e. despiralization, with the beginning of the division of chromosomes intensively spiralizatia and shorter. Maximum circling and shortening chromosome reach in metaphase, when there is a formation of relatively short, dense, rapidly increased basic dyes structures. This stage is most convenient for the study of morphological characteristics of chromosomes.
Metaphase chromosome consists of two longitudinal sub - chromatid [electronic microscopy reveals the structure of chromosomes filament (the so-called chromonema, or graafisella) thickness of 200+, each of which consists of two subunits].
The size of the chromosomes of plants and animals vary widely: from fractions of a micron to tens of microns. The average length of metaphase chromosomes of man lies in the range 1.5 to 10 microns.
Chemical basis of the structure of chromosomes are the nucleoprotein complexes of nucleic acids (see) with the main protein - histones and Protamine.

the structure of the normal chromosomes
Fig. 1. The structure of the normal chromosomes.
A - appearance; - internal structure: 1-primary padding; 2 - secondary street banner; 3-Sputnik; 4 - centromere.

Individual chromosomes (Fig. 1) there are on localization of primary banners, ie, the location of centromere (during mitosis and meiosis to this place attach yarn spindles, pulling it to the pole). In case of loss of centromere fragments of chromosomes lose the ability to break up a division. Primary hauling divides the chromosome 2 shoulder. Depending on the location of the primary banners chromosomes are divided into metacentric (both shoulders equal or nearly equal length), submetacentric (shoulders unequal length) and acrocentric (centromere displaced at the end of chromosomes). In addition to the primary, in the chromosomes can meet less expressed secondary banners. Small tail section of chromosomes, separated secondary tapered, called a satellite.
Each type of organisms characterized by a specific (on number, size and shape of chromosomes) the so-called chromosome set. A set of double or diploid set of chromosomes is designated as a karyotype.

chromosomes are women
Fig. 2. Normal chromosomes are women (in the lower right corner of two X-chromosomes).
chromosome set men
Fig. 3. Normal chromosomal set men in the lower right corner is consistently X - and Y-chromosomes).

In Mature sex cells, egg cells and sperm contains single or haploid set of chromosomes (n)represents half of diploid set (2n)inherent in the chromosomes of all other cells of the body. In a diploid set of each chromosome is represented by a pair of homologues, of which one parent and the other paternal origin. In most cases, the chromosomes of each pair are identical in size, shape and genetic composition. The exceptions are sex chromosomes, which determine the development of the body in male or female direction. Normal chromosomes of man consists of 22 pairs of autosomes and one pair of sex chromosomes. In humans and other mammals female sex is defined by the presence of two X chromosomes, and males have one X and one Y chromosome (Fig. 2 and 3). In the women's cells, one of the X-chromosomes genetically inactive and found in the interphase nucleus in the form of sex chromatin (see). The study of human chromosomes in normal and pathology is the subject of medical cytogenetics. Found that variations in the number or structure of chromosomes from the normal arising in the sex! cells or in early stages of crushing of a fertilized egg, cause disruption of the normal development of the body, causing in some cases, the appearance of parts of spontaneous abortion, stillbirth, congenital malformations and developmental abnormalities after birth (chromosome diseases). Examples of chromosome diseases can serve as a disease syndrome (extra G-chromosome), the syndrome of Kleinfelter (extra X chromosome in males) and Shereshevsky - Turner (absence in the karyotype Y - or one of the X-chromosomes). In medical practice chromosomal analysis of the conduct or direct method (on the cells of bone marrow), or after short-term cultivation of cells outside the body (peripheral blood, skin, embryonic tissue).

Chromosomes (from the Greek. chroma - painting and soma - the body) - filiform, self-replicating structural elements of cell nucleus, containing in the linear order of the genes - genes. Chromosomes are clearly visible in the kernel during division of somatic cells (mitosis) and during division (puberty) to sexual cells, meiosis (Fig. 1). In that and in other case chromosome intensively painted basic dyes and visible on unpainted cytological preparations in phase contrast. In interphase nucleus chromosome despiralization and are not visible in the light microscope, as their transverse dimensions go beyond the resolution of the light microscope. At this time some parts of the chromosomes in the form of thin fibers with diameter 100-500 + can be discerned by means of an electronic microscope. Individual despiralization areas of interphase chromosomes in the nucleus visible through the light microscope as intensively krasaina (heteropolyanions) plots (chromocenters).
Chromosomes are continuously in the cell nucleus, enduring the cycle is reversible circling: mitosis-interphase-mitosis. The main regularities of the structure and behavior of chromosomes during mitosis, meiosis and fertilization same in all organisms.
The chromosome theory of heredity. For the first time chromosome described I. D. Chistyakov in 1874 and Strasburger (that is, Strasburger) in 1879 in 1901 Wilson (E. C. Wilson), and in 1902 Sutton (W. S. Sutton) drew attention to concurrency behavior of chromosomes and Mendelian of genes - genes - in meiosis and fertilization and concluded that genes are located on chromosomes. In 1915-1920, Morgan (I.e. Morgan and his staff made that point, localized in the chromosomes of Drosophila several hundred genes and created a genetic map of chromosomes. Data on the chromosomes received in the first quarter of the 20th century, formed the basis of the chromosome theory of heredity, according to which the succession of signs of cells and organisms in the series of their generations ensured the continuity of their chromosomes.
Chemical composition and autorprojektu chromosomes. In the cytochemical and biochemical studies of chromosomes in 30 and 50-ies of the 20th century established that they consist of permanent components [DNA (see Nucleic acid), basic proteins (histones or Protamine), registoni proteins] and variable components (RNA and associated acidic protein). The basis of chromosomes are deoxyribonucleotide threads with a diameter of about 200 + (Fig. 2)that can connect to the beams with a diameter of 500 A.
The discovery by Watson and Crick (J. D. Watson, F. N. Crick in 1953, the structure of the DNA molecule, its overproduction (reduplication) and nucleic DNA code and development appeared after this molecular genetics has led to the idea of genes as the DNA molecules. (see Genetics). Revealed regularities of overproduction chromosomes [Taylor (J. N. Taylor and others, 1957]caught similar patterns of overproduction DNA molecules (half-conservative reduplication).


Chromosome set is the set of all the chromosomes in a cell. Each species has a characteristic and a regular set of chromosomes, enshrined in the evolution of the species. There are two main types of sets of chromosomes: single, or haploid (in germ cells of animals), denoted by n, and a double or diploid (in somatic cells containing similar couples, homologous chromosomes from the mother and father), denoted by 2n.
Sets of chromosomes species vary greatly in the number of chromosomes: 2 (horse Ascaris) to hundreds and thousands (some spore plants and protozoa). Diploid number of chromosomes of some organisms are: man - 46, gorilla - 48, cats - 60, rat - 42, Drosophila - 8.
The size of chromosomes in different species are also different. The length of chromosomes (in metaphase of mitosis) varies from 0.2 MK some species up to 50 microns, and the diameter of 0.2 to 3 microns.
Morphology of chromosomes is well expressed in metaphase of mitosis. It metaphase chromosomes are used to identify chromosome. These chromosomes are clearly visible both chromatids, which split longitudinally each chromosome and centromere (kinetochore, primary hauling), connecting chromatids (Fig. 3). Centromar seen as the narrowed area, not containing chromatin (see); it mounted thread chromating spindle, so centromar determines the movement of chromosomes to the poles in mitosis and meiosis (Fig. 4).
Loss centromera, such as rupture of chromosomes to ionizing radiation or other mutagens, leads to loss of the ability of a piece of chromosome deprived of centromere (acentricity fragment), participate in mitosis and meiosis and to the loss of the kernel. This can cause severe damage to the cells.
Centromar divides the body of the chromosome into two shoulder. The location of centromere strictly constant for each chromosome and defines three types of chromosomes: 1) acrocentric, or plochodrazni, chromosomes, with one long and the second a very short shoulder, reminding head; 2) submetacentric chromosome long shoulders unequal length; 3) the metacentric chromosomes shoulders with the same or nearly the same length (Fig. 3, 4, 5 and 7).
Characteristics of morphology of certain chromosomes are secondary banners (not having the function centromere), as well as satellites - small plots of chromosomes, United with the rest of her body thin thread (Fig. 5). Sputnica threads have the ability to form the nuclei. Typical structure in the chromosome (chronomere) - thickening or more tightly spiritofyue areas chromosome threads (chromonema). Figure groomer specific to each pair of chromosomes.
The number of chromosomes, their sizes and the form under metafaza characteristic for each type of organism. The combination of these signs of chromosomes is called the karyotype. Karyotype can be represented in the form of a scheme called diagrammoi (see below chromosomes of man).
Sex chromosomes. Genes determining the floor, localized in a special pair of chromosomes are sex chromosomes (mammals, people); in other cases, IOL is determined by the ratio of the number of sex chromosomes and all the rest, called autosomes (Drosophila). In humans, as in other mammals, the female sex is defined by two identical chromosomes, called X-chromosome, males are determined by a pair heteromorş chromosomes: X and Y. the result is reduction division (meiosis) during maturation of oocytes (see Osagent) in women of all eggs contain one X-chromosome. In men the reduction division (maturing) of spermatocyte half of the sperm contains the X chromosome and the other half of the Y-chromosome. The child's sex is determined by random fertilization of an egg by a sperm carrying the X or Y chromosome. The resulting embryo is female (XX) or male (XY) sex. In interphase nucleus women have one X-chromosome is seen as glebka compact sex chromatin.
The functioning of chromosomes and metabolism kernel. Chromosomal DNA is the matrix for the synthesis of specific messenger RNA molecules. This synthesis occurs when the part of chromosome despiralization. Examples of local activation of chromosomes are: education despiralization loops chromosomes in oocytes of birds, amphibians, fishes (the so-called X-tube brushes) and swellings (puffo) loci in Agricultural mnogoznachnykh (polytene) H. salivary secretory glands and other organs of Diptera (Fig. 6). An example of inactivation of entire chromosomes, i.e. disable it from the metabolism of the cells, is the formation of one of the X-chromosomes compact body of sex chromatin.
The opening of the mechanisms of functioning of polytene X. type tube brushes and other types circling and despiralization Agriculture is crucial for understanding reversible differential gene activation.
Human chromosome. In 1922 the painter (I. S. Painter) established the diploid number of chromosomes (spermatogonia)equal to 48. In 1956, Tio, and Lebanon (N. J. Tjio, A. Levan) used a set of new methods of research of Agricultural person: cell culture; research Agricultural without histological sections on total drugs cells; colchicine leading to stop mitoses at metaphase and accumulation of such metaphases; phytohemagglutinin, stimulating the introduction of cells in mitosis; treatment of metaphase cells hypotonic salt solution. All this helped to determine the diploid number of chromosomes in humans (it was equal to 46) and give the description of the human karyotype. In 1960 in Denver (USA), the international Commission has developed a range of human chromosomes. According to the Commission proposal, the term "fetuses" should be applied to the systematic collection of Agricultural single cell (Fig. 7 and 8). The term "idiotami" is retained to represent about a set X. in the form of diagrams constructed on the basis of measurements and descriptions of the morphology of Agricultural multiple cells.
X. human numbered (partly serially) from 1 to 22 in accordance with the features of morphology, allowing their identification. Sex X. do not have numbers and are denoted as X and Y (Fig. 8).
The connection of a number of diseases and birth defects in human development with changes in the number and the structure of its Agriculture (see Heredity).
Cm. also Cytogenetic studies.
All these achievements have created a solid basis for the development cytogenetics of human rights.

Fig. 1. Chromosome: a - on stage anafazy mitosis in microsporocytes trefoil; - at metaphase first division of meiosis in pollen mother cells of tradescantia. In both cases you can see the spiral structure of chromosomes.
Fig. 2. Elementary chromosome threads with a diameter of 100 + (DNA + histone) of the interphase nuclei of the thymus gland calf (electron microscopy)And isolated from the nuclei of the thread; - A thin slice through the film of the same drug.
Fig. 3. Chromosome set Vicia faba (horse beans) in metaphase.
Fig. 4. The scheme of the structure of chromosomes in metaphase of mitosis after longitudinal splitting centromere: a and A1 - sister chromatids; 1 - long arm; 2 - short arm; 3 - secondary hauling; 4 - centromar; 5 - spindle fibers.
Fig. 5. The scheme of the morphology of chromosomes in the anaphase mitosis (chromatid. outgoing to the pole). A - appearance of a chromosome; - the internal structure of the same chromosome with two components her chromonema (programatically): 1 - primary hauling with chronomere that make up centromar; 2 - secondary street banner; 3 - satellite; 4 - thread satellite.
Fig. 6. Polytene chromosomes two-winged insect Acriscotopus lucidus: a and B is the area enclosed by the dotted lines, intense functioning (unbounded); In the same area in the defunct state. Numbers denote separate loci of chromosomes (chronomere).
Fig. 7. Chromosome set in the culture of peripheral blood leukocytes men (2n=46).
Fig. 8. Chromosomes are the same as in Fig. 7, set, systematized according dangerously item in pairs homologues (karyotype).