Chromosomes, their structure, types, types, meaning. Structure and functions of chromosomes. Reproduction in the organic world. The structure of germ cells

The most important organelles of the cell are microscopic structures located in the core. They were discovered simultaneously by several scientists, including Russian biologist Ivan Chistyakov.

The name of the new cellular component was not immediately invented. He gave it German scientist W. Waldeyer, who, while staining histological preparations, discovered certain bodies that stained well with fuchsin. At that time it was not yet known exactly what role chromosomes play.

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Meaning

Structure

Let's consider what structure and functions these unique cellular formations have. In the interphase state they are practically invisible. At this stage, the molecule doubles and forms two sister chromatids.

The structure of a chromosome can be examined at the time of its preparation for mitosis or meiosis (division). Such chromosomes are called metaphase, because they are formed at the stage of metaphase, preparation for division. Until this moment, the bodies are inconspicuous thin dark threads which are called chromatin.

During the transition to the metaphase stage, the structure of the chromosome changes: it is formed by two chromatids connected by a centromere - this is called primary constriction. During cell division the amount of DNA also doubles. The schematic drawing resembles the letter X. They contain, in addition to DNA, proteins (histone, non-histone) and ribonucleic acid - RNA.

The primary constriction divides the cell body (nucleoprotein structure) into two arms, slightly bending them. Based on the location of the constriction and the length of the arms, the following classification of types was developed:

metacentric, they are also equal-armed, the centromere divides the cell exactly in half;
submetacentric. Shoulders are not the same, the centromere is shifted closer to one end;
acrocentric. The centromere is strongly shifted and is located almost at the edge;
telocentric. One shoulder is completely missing does not occur in humans.

Some species have secondary constriction, which can be located at different points. It separates a part called the satellite. It differs from the primary one in that has no visible angle between segments. Its function is to synthesize RNA on a DNA template. It occurs in people in 13, 14, 21 and 15, 21 and 22 pairs of chromosomes. Appearing in another couple carries the risk of serious illness.

Now let's look at what function the chromosomes perform. Thanks to reproduction different types mRNA and proteins they carry out clear control over all processes of cell life and the body as a whole. Chromosomes in the nucleus of eukaryotes perform the functions of synthesizing proteins from amino acids, carbohydrates from inorganic compounds, breaking down organic substances into inorganic ones, store and transmit hereditary information.

Diploid and haploid sets

The specific structure of chromosomes may differ depending on where they are formed. What is the name of the set of chromosomes in somatic cell structures? It is called diploid or double. Somatic cells reproduce by simple division into two daughters. In ordinary cellular formations, each cell has its own homologous pair. This happens because each of the daughter cells must have the same volume of hereditary information, as the mother's.

How do the number of chromosomes in somatic and germ cells compare? Here the numerical ratio is two to one. During the formation of germ cells, special type of division, as a result, the set in mature eggs and sperm becomes single. What function chromosomes perform can be explained by studying the features of their structure.

Male and female reproductive cells have half set called haploid, that is, there are 23 of them in total. The sperm merges with the egg, resulting in a new organism with a complete set. The genetic information of a man and a woman is thus combined. If germ cells carried a diploid set (46), then when united, the result would be non-viable organism.

Genome diversity

The number of carriers of genetic information differs among different classes and species of living beings.

They have the ability to be painted with specially selected dyes; they alternate in their structure light and dark transverse sections - nucleotides. Their sequence and location are specific. Thanks to this, scientists have learned to distinguish cells and, if necessary, clearly indicate the “broken” one.

Currently, geneticists deciphered the person and compiled genetic maps, which allows the analysis method to suggest some serious hereditary diseases even before they appear.

There is now an opportunity to confirm paternity, determine ethnicity, to identify whether a person is a carrier of any pathology that has not yet manifested itself or is dormant inside the body, to determine the characteristics negative reaction to medications and much more.

A little about pathology

During the transfer of the gene set, there may be failures and mutations, leading to serious consequences, among them are

deletions - loss of one section of the shoulder, causing underdevelopment of organs and brain cells;
inversions - processes in which a fragment is flipped 180 degrees, the result is incorrect gene sequence;
duplications – bifurcation of a section of the shoulder.

Mutations can also occur between adjacent bodies - this phenomenon was called translocation. The well-known Down, Patau, and Edwards syndromes are also a consequence disruption of the gene apparatus.

Chromosomal diseases. Examples and reasons

Classification of cells and chromosomes

Conclusion

The importance of chromosomes is great. Without these tiny ultrastructures transfer of genetic information is impossible, therefore, the organisms will not be able to reproduce. Modern technologies can read the code embedded in them and successfully prevent possible diseases which were previously considered incurable.

). Chromatin is heterogeneous, and some types of such heterogeneity are visible under a microscope. The fine structure of chromatin in the interphase nucleus, determined by the nature of DNA folding and its interaction with proteins, plays an important role in the regulation of gene transcription and DNA replication and, possibly, cellular differentiation.

The sequences of DNA nucleotides that form genes and serve as a template for the synthesis of mRNA are distributed along the entire length of the chromosomes (individual genes, of course, are too small to be seen under a microscope). By the end of the 20th century, for approximately 6,000 genes, it was established on which chromosome and in which part of the chromosome they are located and what the nature of their linkage is (that is, their position relative to each other).

The heterogeneity of metaphase chromosomes, as already mentioned, can be seen even with light microscopy. Differential staining of at least 12 chromosomes revealed differences in the width of some bands between homologous chromosomes (Fig. 66.3). Such polymorphic regions consist of non-coding highly repetitive DNA sequences.

The methods of molecular genetics have made it possible to identify a huge number of smaller polymorphic DNA regions that are therefore undetectable by light microscopy. These regions are identified as restriction fragment length polymorphism, tandem repeats varying in number, and short tandem repeat polymorphism (mono-, di-, tri-, and tetranucleotide). Such variability usually does not manifest itself phenotypically.

However, polymorphism serves as a convenient tool for prenatal diagnosis due to the linkage of certain markers with mutant genes that cause diseases (for example, in Duchenne myopathy), as well as in establishing the zygosity of twins, establishing paternity, and predicting transplant rejection.

It is difficult to overestimate the importance of such markers, especially highly polymorphic short tandem repeats that are widespread in the genome, for mapping the human genome. In particular, they make it possible to establish the exact order and nature of the interaction of loci that play an important role in ensuring normal ontogenesis and cell differentiation. This also applies to those loci in which mutations lead to hereditary diseases.

Microscopically visible regions on the short arm of acrocentric autosomes (Fig. 66.1) provide rRNA synthesis and the formation of nucleoli, which is why they are called nucleolar organizer regions. In metaphase they are not condensed and do not stain. The regions of the nucleolar organizer are adjacent to the condensed sections of chromatin - satellites - located at the end of the short arm of the chromosome. Satellites do not contain genes and are polymorphic regions.

In a small proportion of cells, it is possible to identify other areas decondensed in metaphase, the so-called fragile areas, where “complete” chromosome breaks can occur. Abnormalities in the only such region located at the end of the long arm of the X chromosome are of clinical significance. Such disorders cause fragile X syndrome.

Other examples of specialized regions of chromosomes are telomeres and centromeres.

The role of heterochromatin, which accounts for a significant part of the human genome, has not yet been precisely established. Heterochromatin is condensed throughout almost the entire cell cycle, it is inactive and replicates late. Most regions are condensed and inactive in all cells (), although others, such as the X chromosome, can be either condensed and inactive or decondensed and active (facultative heterochromatin). If, due to chromosomal aberrations, genes end up close to heterochromatin, then the activity of such genes can change or even be blocked. Therefore, the manifestations of chromosomal aberrations, such as duplications or deletions, depend not only on the affected loci, but also on the type of chromatin in them. Many chromosomal abnormalities that are not lethal affect inactive or inactivated regions of the genome. This may explain that trisomy on some chromosomes or monosomy on the X chromosome are compatible with life.

Manifestations of chromosomal abnormalities also depend on the new arrangement of structural and regulatory genes in relation to each other and to heterochromatin.

Fortunately, many structural features of chromosomes can be reliably detected by cytological methods. Currently, there are a number of methods for differential chromosome staining (Fig. 66.1 and Fig. 66.3). The location and width of the bands are identical in each pair of homologous chromosomes, with the exception of polymorphic regions, so staining can be used in clinical cytogenetics to identify chromosomes and detect structural abnormalities in them.

Chromosomes are the main structural elements of the cell nucleus, which are carriers of genes in which hereditary information is encoded. Having the ability to reproduce themselves, chromosomes provide a genetic link between generations.

The morphology of chromosomes is related to the degree of their spiralization. For example, if at the stage of interphase (see Mitosis, Meiosis) the chromosomes are maximally unfolded, i.e., despiralized, then with the beginning of division the chromosomes intensively spiralize and shorten. Maximum spiralization and shortening of chromosomes is achieved at the metaphase stage, when relatively short, dense structures that are intensely stained with basic dyes are formed. This stage is most convenient for studying the morphological characteristics of chromosomes.

The metaphase chromosome consists of two longitudinal subunits - chromatids [reveals elementary threads in the structure of chromosomes (the so-called chromonemas, or chromofibrils) 200 Å thick, each of which consists of two subunits].

The sizes of plant and animal chromosomes vary significantly: from fractions of a micron to tens of microns. The average lengths of human metaphase chromosomes range from 1.5-10 microns.

The chemical basis of the structure of chromosomes are nucleoproteins - complexes (see) with the main proteins - histones and protamines.

Rice. 1. The structure of a normal chromosome.
A - appearance; B - internal structure: 1-primary constriction; 2 - secondary constriction; 3 - satellite; 4 - centromere.

Individual chromosomes (Fig. 1) are distinguished by the localization of the primary constriction, i.e., the location of the centromere (during mitosis and meiosis, spindle threads are attached to this place, pulling it towards the pole). When a centromere is lost, chromosome fragments lose their ability to separate during division. The primary constriction divides the chromosomes into 2 arms. Depending on the location of the primary constriction, chromosomes are divided into metacentric (both arms are equal or almost equal in length), submetacentric (arms of unequal length) and acrocentric (the centromere is shifted to the end of the chromosome). In addition to the primary one, less pronounced secondary constrictions may be found in chromosomes. A small terminal section of chromosomes, separated by a secondary constriction, is called a satellite.

Each type of organism is characterized by its own specific (in terms of the number, size and shape of chromosomes) so-called chromosome set. The totality of a double, or diploid, set of chromosomes is designated as a karyotype.

Rice. 2. Normal chromosome set of a woman (two X chromosomes in the lower right corner).

Rice. 3. The normal chromosome set of a man (in the lower right corner - X and Y chromosomes in sequence).

Mature eggs contain a single, or haploid, set of chromosomes (n), which makes up half of the diploid set (2n) inherent in the chromosomes of all other cells of the body. In the diploid set, each chromosome is represented by a pair of homologues, one of which is of maternal and the other of paternal origin. In most cases, the chromosomes of each pair are identical in size, shape and gene composition. The exception is sex chromosomes, the presence of which determines the development of the body in a male or female direction. The normal human chromosome set consists of 22 pairs of autosomes and one pair of sex chromosomes. In humans and other mammals, female is determined by the presence of two X chromosomes, and male by one X and one Y chromosome (Fig. 2 and 3). In female cells, one of the X chromosomes is genetically inactive and is found in the interphase nucleus in the form (see). The study of human chromosomes in health and disease is the subject of medical cytogenetics. It has been established that deviations in the number or structure of chromosomes from the norm that occur in reproductive organs! cells or in the early stages of fragmentation of a fertilized egg, cause disturbances in the normal development of the body, causing in some cases the occurrence of some spontaneous abortions, stillbirths, congenital deformities and developmental abnormalities after birth (chromosomal diseases). Examples of chromosomal diseases include Down's disease (an extra G chromosome), Klinefelter's syndrome (an extra X chromosome in men) and (the absence of a Y or one of the X chromosomes in the karyotype). In medical practice, chromosomal analysis is carried out either directly (on bone marrow cells) or after short-term cultivation of cells outside the body (peripheral blood, skin, embryonic tissue).

Chromosomes (from the Greek chroma - color and soma - body) are thread-like, self-reproducing structural elements of the cell nucleus, containing factors of heredity - genes - in a linear order. Chromosomes are clearly visible in the nucleus during the division of somatic cells (mitosis) and during the division (maturation) of germ cells - meiosis (Fig. 1). In both cases, chromosomes are intensely stained with basic dyes and are also visible on unstained cytological preparations in phase contrast. In the interphase nucleus, the chromosomes are despiralized and are not visible in a light microscope, since their transverse dimensions exceed the resolution limits of the light microscope. At this time, individual sections of chromosomes in the form of thin threads with a diameter of 100-500 Å can be distinguished using an electron microscope. Individual non-despiralized sections of chromosomes in the interphase nucleus are visible through a light microscope as intensely stained (heteropyknotic) areas (chromocenters).

Chromosomes continuously exist in the cell nucleus, undergoing a cycle of reversible spiralization: mitosis-interphase-mitosis. The basic patterns of the structure and behavior of chromosomes in mitosis, meiosis and during fertilization are the same in all organisms.

Chromosomal theory of heredity. Chromosomes were first described by I. D. Chistyakov in 1874 and E. Strasburger in 1879. In 1901, E. V. Wilson, and in 1902, W. S. Sutton, drew attention to parallelism in the behavior of chromosomes and Mendelian factors of heredity - genes - in meiosis and during fertilization and came to the conclusion that genes are located in chromosomes. In 1915-1920 Morgan (T.N. Morgan) and his collaborators proved this position, localized several hundred genes in Drosophila chromosomes and created genetic maps of the chromosomes. Data on chromosomes obtained in the first quarter of the 20th century formed the basis of the chromosomal theory of heredity, according to which the continuity of the characteristics of cells and organisms in a number of their generations is ensured by the continuity of their chromosomes.

Chemical composition and autoreproduction of chromosomes. As a result of cytochemical and biochemical studies of chromosomes in the 30s and 50s of the 20th century, it was established that they consist of constant components [DNA (see Nucleic acids), basic proteins (histones or protamines), non-histone proteins] and variable components (RNA and acidic protein associated with it). The basis of chromosomes is made up of deoxyribonucleoprotein threads with a diameter of about 200 Å (Fig. 2), which can be connected into bundles with a diameter of 500 Å.

The discovery by Watson and Crick (J. D. Watson, F. N. Crick) in 1953 of the structure of the DNA molecule, the mechanism of its autoreproduction (reduplication) and the nucleic code of DNA and the development of molecular genetics that arose after this led to the idea of genes as sections of the DNA molecule. (see Genetics). The patterns of autoreproduction of chromosomes were revealed [Taylor (J. N. Taylor) et al., 1957], which turned out to be similar to the patterns of autoreproduction of DNA molecules (semi-conservative reduplication).

Chromosome set- the totality of all chromosomes in a cell. Each biological species has a characteristic and constant set of chromosomes, fixed in the evolution of this species. There are two main types of sets of chromosomes: single, or haploid (in animal germ cells), denoted n, and double, or diploid (in somatic cells, containing pairs of similar, homologous chromosomes from the mother and father), denoted 2n.

The sets of chromosomes of individual biological species vary significantly in the number of chromosomes: from 2 (horse roundworm) to hundreds and thousands (some spore plants and protozoa). The diploid chromosome numbers of some organisms are as follows: humans - 46, gorillas - 48, cats - 60, rats - 42, fruit flies - 8.

The sizes of chromosomes also vary between species. The length of chromosomes (in metaphase of mitosis) varies from 0.2 microns in some species to 50 microns in others, and the diameter from 0.2 to 3 microns.

The morphology of chromosomes is well expressed in metaphase of mitosis. It is metaphase chromosomes that are used to identify chromosomes. In such chromosomes, both chromatids are clearly visible, into which each chromosome and the centromere (kinetochore, primary constriction) connecting the chromatids are longitudinally split (Fig. 3). The centromere is visible as a narrowed area that does not contain chromatin (see); the threads of the achromatin spindle are attached to it, due to which the centromere determines the movement of chromosomes to the poles in mitosis and meiosis (Fig. 4).

Loss of a centromere, for example when a chromosome is broken by ionizing radiation or other mutagens, leads to the loss of the ability of the piece of chromosome lacking the centromere (acentric fragment) to participate in mitosis and meiosis and to its loss from the nucleus. This can cause severe cell damage.

The centromere divides the chromosome body into two arms. The location of the centromere is strictly constant for each chromosome and determines three types of chromosomes: 1) acrocentric, or rod-shaped, chromosomes with one long and a second very short arm, resembling a head; 2) submetacentric chromosomes with long arms of unequal length; 3) metacentric chromosomes with arms of the same or almost the same length (Fig. 3, 4, 5 and 7).

Rice. 4. Scheme of chromosome structure in metaphase of mitosis after longitudinal splitting of the centromere: A and A1 - sister chromatids; 1 - long shoulder; 2 - short shoulder; 3 - secondary constriction; 4- centromere; 5 - spindle fibers.

Characteristic features of the morphology of certain chromosomes are secondary constrictions (which do not have the function of a centromere), as well as satellites - small sections of chromosomes connected to the rest of its body by a thin thread (Fig. 5). Satellite filaments have the ability to form nucleoli. The characteristic structure in the chromosome (chromomeres) is thickening or more tightly coiled sections of the chromosomal thread (chromonemas). The chromomere pattern is specific to each pair of chromosomes.

Rice. 5. Scheme of chromosome morphology in anaphase of mitosis (chromatid extending to the pole). A - appearance of the chromosome; B - internal structure of the same chromosome with its two constituent chromonemas (hemichromatids): 1 - primary constriction with chromomeres constituting the centromere; 2 - secondary constriction; 3 - satellite; 4 - satellite thread.

The number of chromosomes, their size and shape at the metaphase stage are characteristic of each type of organism. The combination of these characteristics of a set of chromosomes is called a karyotype. A karyotype can be represented in a diagram called an idiogram (see human chromosomes below).

Sex chromosomes. Genes that determine sex are localized in a special pair of chromosomes - sex chromosomes (mammals, humans); in other cases, the iol is determined by the ratio of the number of sex chromosomes and all others, called autosomes (Drosophila). In humans, as in other mammals, the female sex is determined by two identical chromosomes, designated as X chromosomes, the male sex is determined by a pair of heteromorphic chromosomes: X and Y. As a result of reduction division (meiosis) during the maturation of oocytes (see Oogenesis) in women all eggs contain one X chromosome. In men, as a result of the reduction division (maturation) of spermatocytes, half of the sperm contains an X chromosome, and the other half a Y chromosome. The sex of a child is determined by the accidental fertilization of an egg by a sperm carrying an X or Y chromosome. The result is a female (XX) or male (XY) embryo. In the interphase nucleus of women, one of the X chromosomes is visible as a clump of compact sex chromatin.

Chromosome functioning and nuclear metabolism. Chromosomal DNA is the template for the synthesis of specific messenger RNA molecules. This synthesis occurs when a given region of the chromosome is despiraled. Examples of local chromosome activation are: the formation of despiralized chromosome loops in the oocytes of birds, amphibians, fish (the so-called X-lamp brushes) and swellings (puffs) of certain chromosome loci in multi-stranded (polytene) chromosomes of the salivary glands and other secretory organs of dipteran insects (Fig. 6). An example of inactivation of an entire chromosome, i.e., its exclusion from the metabolism of a given cell, is the formation of one of the X chromosomes of a compact body of sex chromatin.

Rice. 6. Polytene chromosomes of the dipteran insect Acriscotopus lucidus: A and B - area limited by dotted lines, in a state of intensive functioning (puff); B - the same area in a non-functioning state. The numbers indicate individual chromosome loci (chromomeres).
Rice. 7. Chromosome set in a culture of male peripheral blood leukocytes (2n=46).

Revealing the mechanisms of functioning of lampbrush-type polytene chromosomes and other types of chromosome spiralization and despiralization is crucial for understanding reversible differential gene activation.

Human chromosomes. In 1922, T. S. Painter established the diploid number of human chromosomes (in spermatogonia) to be 48. In 1956, Tio and Levan (N. J. Tjio, A. Levan) used a set of new methods for studying human chromosomes : cell culture; study of chromosomes without histological sections on whole cell preparations; colchicine, which leads to the arrest of mitoses at the metaphase stage and the accumulation of such metaphases; phytohemagglutinin, which stimulates the entry of cells into mitosis; treatment of metaphase cells with hypotonic saline solution. All this made it possible to clarify the diploid number of chromosomes in humans (it turned out to be 46) and provide a description of the human karyotype. In 1960, in Denver (USA), an international commission developed a nomenclature for human chromosomes. According to the commission's proposals, the term "karyotype" should be applied to the systematic set of chromosomes of a single cell (Fig. 7 and 8). The term "idiotram" is retained to represent the set of chromosomes in the form of a diagram constructed from measurements and descriptions of the chromosome morphology of several cells.

Human chromosomes are numbered (somewhat serially) from 1 to 22 in accordance with the morphological features that allow their identification. Sex chromosomes do not have numbers and are designated as X and Y (Fig. 8).

A connection has been discovered between a number of diseases and birth defects in human development with changes in the number and structure of its chromosomes. (see Heredity).

History of the discovery of chromosomes

Back in the middle of the 19th century before last, many biologists, studying the structure of plant and animal cells, drew attention to thin threads and tiny ring-shaped structures in the nucleus of some cells. And so the German scientist Walter Fleming used aniline dyes to treat the nuclear structures of the cell, which is called “officially” opens the chromosomes. More precisely, he named the discovered substance “chromatid” for its ability to stain, and the term “chromosomes” was introduced into use a little later (in 1888) by another German scientist, Heinrich Wilder. The word "chromosome" comes from the Greek words "chroma" - color and "somo" - body.

Chromosomal theory of heredity

Of course, the history of the study of chromosomes did not end with their discovery; in 1901-1902, American scientists Wilson and Saton, independently of each other, drew attention to the similarity in the behavior of chromosomes and Mendeleev’s factors of heredity - genes. As a result, scientists came to the conclusion that genes are located in chromosomes and it is through them that genetic information is transmitted from generation to generation, from parents to children.

In 1915-1920, the participation of chromosomes in gene transmission was proven in practice in a series of experiments carried out by the American scientist Morgan and his laboratory staff. They managed to localize several hundred hereditary genes in the chromosomes of the Drosophila fly and create genetic maps of the chromosomes. Based on these data, the chromosomal theory of heredity was created.

Chromosome structure

The structure of chromosomes varies depending on the species, so the metaphase chromosome (formed in the metaphase stage during cell division) consists of two longitudinal threads - chromatids, which connect at a point called the centromere. A centromere is a region of a chromosome that is responsible for the separation of sister chromatids into daughter cells. It also divides the chromosome into two parts, called the short and long arms, and is also responsible for the division of the chromosome, since it contains a special substance - the kinetochore, to which the spindle structures are attached.

Here the picture shows the visual structure of a chromosome: 1. chromatids, 2. centromere, 3. short chromatid arm, 4. long chromatid arm. At the ends of the chromatids there are telomeres, special elements that protect the chromosome from damage and prevent fragments from sticking together.

Shapes and types of chromosomes

The sizes of plant and animal chromosomes vary significantly: from fractions of a micron to tens of microns. The average lengths of human metaphase chromosomes range from 1.5 to 10 microns. Depending on the type of chromosome, its staining abilities also differ. Depending on the location of the centromere, the following forms of chromosomes are distinguished:

Metacentric chromosomes, which are characterized by a central location of the centromere.
Submetacentric, they are characterized by an uneven arrangement of chromatids, when one arm is longer and the other is shorter.
Acrocentric or rod-shaped. Their centromere is located almost at the very end of the chromosome.

Functions of chromosomes

The main functions of chromosomes, both for animals and plants and all living beings in general, are the transfer of hereditary, genetic information from parents to children.

Set of chromosomes

The importance of chromosomes is so great that their number in cells, as well as the characteristics of each chromosome, determine the characteristic feature of a particular biological species. So, for example, the Drosophila fly has 8 chromosomes, the y has 48, and the human chromosome set is 46 chromosomes.

In nature, there are two main types of chromosome sets: single or haploid (found in germ cells) and double or diploid. The diploid set of chromosomes has a pair structure, that is, the entire set of chromosomes consists of chromosome pairs.

Human chromosome set

As we wrote above, the cells of the human body contain 46 chromosomes, which are combined into 23 pairs. All together they make up the human chromosome set. The first 22 pairs of human chromosomes (they are called autosomes) are common to both men and women, and only 23 pairs - sex chromosomes - vary between sexes, which also determines a person’s gender. The set of all pairs of chromosomes is also called a karyotype.

The human chromosome set has this type, 22 pairs of double diploid chromosomes contain all our hereditary information, and the last pair differs, in men it consists of a pair of conditional X and Y sex chromosomes, while in women there are two X chromosomes.

All animals have a similar structure of the chromosome set, only the number of non-sex chromosomes in each of them is different.

Genetic diseases associated with chromosomes

A malfunction of chromosomes, or even their incorrect number itself, is the cause of many genetic diseases. For example, Down syndrome appears due to the presence of an extra chromosome in the human chromosome set. And such genetic diseases as color blindness and hemophilia are caused by malfunctions of existing chromosomes.

Chromosomes, video

And finally, an interesting educational video about chromosomes.

A chromosome is an elongated, structured collection of genes that carries information about heredity and is formed from condensed. Chromatin is made up of DNA and proteins that are tightly packed together to form chromatin fibers. Condensed chromatin fibers form chromosomes. Chromosomes are located in our. The sets of chromosomes join together (one from the mother and one from the father) and are known as .

Scheme of chromosome structure at the metaphase stage

Unduplicated chromosomes are single-stranded and consist of a region that connects the chromosome arms. The short arm is indicated by the letter p, and the long one is a letter q. The terminal regions of chromosomes are called telomeres, which consist of repeated non-coding DNA sequences that are shortened during cell division.

Chromosome duplication

Chromosomal duplication occurs before division processes through or. DNA replication processes allow the correct number of chromosomes to be maintained after the parent cell divides. A duplicated chromosome consists of two identical chromosomes, called chromosomes, which are linked at the centromere. The sisters remain together until the end of the division process, where they are separated by spindle fibers and enclosed in. Once paired chromatids are separated from each other, each of them becomes .

Chromosomes and cell division

One of the most important elements of successful cell division is the correct distribution of chromosomes. In mitosis, this means that the chromosomes must be distributed between the two daughter cells. In meiosis, chromosomes are distributed among four daughter cells. The spindle is responsible for moving chromosomes during cell division.

This type of cell movement involves interactions between spindle microtubules and motor proteins working together to separate chromosomes. It is vital that the correct number of chromosomes is retained in the daughter cells. Errors that occur during cell division can result in unbalanced chromosome numbers, having too many or not enough chromosomes. This abnormality is known as aneuploidy and can occur on autosomal chromosomes during mitosis or on sex chromosomes during meiosis. Abnormalities in chromosomal numbers can lead to birth defects, developmental disorders and death.

Chromosomes and protein production

Protein production is a vital cellular process that depends on DNA and chromosomes. DNA contains segments called genes that code for proteins. During protein production, the DNA is unwound and its coding segments are transcribed into an RNA transcript. The RNA transcript is then translated to form a protein.

Chromosome mutation

Chromosome mutations are changes that occur in chromosomes and are usually the result of errors that occur during meiosis or when exposed to mutagens such as chemicals or radiation.

Chromosome breakage and duplication can lead to several types of chromosome structural changes that are usually harmful to humans. These types of mutations result in chromosomes with extra genes that are in the wrong sequence. Mutations can also produce cells with the wrong number of chromosomes. Abnormal chromosome numbers usually result from nondisjunction or disruption of homologous chromosomes during meiosis.