Chromosome is a thread-like structure containing DNA in the cell nucleus, which carries genes, units of heredity, arranged in a linear order. Humans have 22 pairs of regular chromosomes and one pair of sex chromosomes. In addition to genes, chromosomes also contain regulatory elements and nucleotide sequences. They house DNA-binding proteins that control DNA functions. Interestingly, the word "chromosome" comes from the Greek word "chrome", meaning "color". Chromosomes received this name because they have the ability to be colored in different tones. The structure and nature of chromosomes vary from organism to organism. Human chromosomes have always been a subject of constant interest to researchers working in the field of genetics. The wide range of factors that are determined by human chromosomes, the abnormalities for which they are responsible, and their complex nature have always attracted the attention of many scientists.
Interesting facts about human chromosomes
Human cells contain 23 pairs of nuclear chromosomes. Chromosomes are made up of DNA molecules that contain genes. The chromosomal DNA molecule contains three nucleotide sequences required for replication. When chromosomes are stained, the banded structure of mitotic chromosomes becomes apparent. Each strip contains numerous DNA nucleotide pairs.
Humans are a sexually reproducing species with diploid somatic cells containing two sets of chromosomes. One set is inherited from the mother, while the other is inherited from the father. Reproductive cells, unlike body cells, have one set of chromosomes. Crossing over between chromosomes leads to the creation of new chromosomes. New chromosomes are not inherited from either parent. This accounts for the fact that not all of us exhibit traits that we receive directly from one of our parents.
Autosomal chromosomes are assigned numbers from 1 to 22 in descending order as their size decreases. Each person has two sets of 22 chromosomes, an X chromosome from the mother and an X or Y chromosome from the father.
An abnormality in the contents of a cell's chromosomes can cause certain genetic disorders in people. Chromosomal abnormalities in people are often responsible for the occurrence of genetic diseases in their children. Those who have chromosomal abnormalities are often only carriers of the disease, while their children develop the disease.
Chromosomal aberrations (structural changes in chromosomes) are caused by various factors, namely deletion or duplication of part of a chromosome, inversion, which is a change in the direction of a chromosome to the opposite, or translocation, in which part of a chromosome is torn off and attached to another chromosome.
An extra copy of chromosome 21 is responsible for a very well known genetic disorder called Down syndrome.
Trisomy 18 results in Edwards syndrome, which can cause death in infancy.
Deletion of part of the fifth chromosome results in a genetic disorder known as Cri-Cat Syndrome. People affected by this disease often have mental retardation and their crying in childhood resembles that of a cat.
Disorders caused by sex chromosome abnormalities include Turner syndrome, in which female sexual characteristics are present but characterized by underdevelopment, as well as XXX syndrome in girls and XXY syndrome in boys, which cause dyslexia in affected individuals.
Chromosomes were first discovered in plant cells. Van Beneden's monograph on fertilized roundworm eggs led to further research. August Weissman later showed that the germ line was distinct from the soma and discovered that cell nuclei contained hereditary material. He also suggested that fertilization leads to the formation of a new combination of chromosomes.
These discoveries became cornerstones in the field of genetics. Researchers have already accumulated a significant amount of knowledge about human chromosomes and genes, but much remains to be discovered.
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Containing genes. The name "chromosome" comes from the Greek words (chrōma - color, color and sōma - body), and is due to the fact that when cells divide, they become intensely colored in the presence of basic dyes (for example, aniline).
Many scientists, since the beginning of the 20th century, have thought about the question: “How many chromosomes does a person have?” So, until 1955, all the “minds of humanity” were convinced that the number of chromosomes in humans is 48, i.e. 24 pairs. The reason was that Theophilus Painter (Texas scientist) incorrectly counted them in preparative sections of human testes, according to a court decision (1921). Subsequently, other scientists, using different calculation methods, also came to this opinion. Even after developing a method for separating chromosomes, the researchers did not challenge Painter’s result. The error was discovered by scientists Albert Levan and Jo-Hin Thio in 1955, who accurately calculated how many pairs of chromosomes a person has, namely 23 (more modern technology was used to count them).
Somatic and germ cells contain a different chromosome set in biological species, which cannot be said about the morphological characteristics of chromosomes, which are constant. have a doubled (diploid set), which is divided into pairs of identical (homologous) chromosomes, which are similar in morphology (structure) and size. One part is always of paternal origin, the other of maternal origin. Human sex cells (gametes) are represented by a haploid (single) set of chromosomes. When an egg is fertilized, haploid sets of female and male gametes are united in one zygote nucleus. In this case, the double dialing is restored. It is possible to say with accuracy how many chromosomes a person has - there are 46 of them, with 22 pairs of them being autosomes and one pair being sex chromosomes (gonosomes). Sexes have differences - both morphological and structural (gene composition). In a female organism, a pair of gonosomes contains two X chromosomes (XX-pair), and in a male organism, one X- and a Y-chromosome (XY-pair).
Morphologically, chromosomes change during cell division, when they double (with the exception of germ cells, in which duplication does not occur). This is repeated many times, but no change in the chromosome set is observed. Chromosomes are most noticeable at one of the stages of cell division (metaphase). During this phase, the chromosomes are represented by two longitudinally split formations (sister chromatids), which narrow and unite in the area of the so-called primary constriction, or centromere (an obligatory element of the chromosome). Telomeres are the ends of a chromosome. Structurally, human chromosomes are represented by DNA (deoxyribonucleic acid), which encodes the genes that make up them. Genes, in turn, carry information about a specific trait.
Individual development will depend on how many chromosomes a person has. There are such concepts as: aneuploidy (change in the number of individual chromosomes) and polyploidy (the number of haploid sets is greater than the diploid one). The latter can be of several types: loss of a homologous chromosome (monosomy), or appearance (trisomy - one extra, tetrasomy - two extra, etc.). All this is a consequence of genomic and chromosomal mutations, which can lead to pathological conditions such as Klinefelter syndrome, Shereshevsky-Turner syndrome and other diseases.
Thus, only the twentieth century gave answers to all questions, and now every educated inhabitant of planet Earth knows how many chromosomes a person has. The sex of the unborn child depends on the composition of the 23 pairs of chromosomes (XX or XY), and this is determined during fertilization and the fusion of the female and male reproductive cells.
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. The small terminal portion of the 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).
See also Cytogenetic studies.
All these achievements have created a solid basis for the development of human cytogenetics.
Rice. 1. Chromosomes: A - at the anaphase stage of mitosis in trefoil microsporocytes; B - at the metaphase stage of the first meiotic division in the pollen mother cells of Tradescantia. In both cases, the spiral structure of the chromosomes is visible.
Rice. 2. Elementary chromosomal threads with a diameter of 100 Å (DNA + histone) from interphase nuclei of the calf thymus gland (electron microscopy): A - threads isolated from nuclei; B - thin section through the film of the same preparation.
Rice. 3. Chromosome set of Vicia faba (faba bean) at the metaphase stage.
Rice. 8. Chromosomes are the same as in Fig. 7, sets, systematized according to the Denver nomenclature into pairs of homologues (karyotype).
32. Mitotic chromosomes. Morphological organization and functions. Karyotype (using the example of a person).
Mitotic chromosomes are formed in a cell during mitosis. These are non-functioning chromosomes, and the DNA molecules in them are packed extremely tightly. Suffice it to say that the total length of metaphase chromosomes is approximately 104 times less than the length of all DNA contained in the nucleus. Due to this compactness of mitotic chromosomes, an even distribution of genetic material between daughter cells during mitosis is ensured. Karyotype- a set of characteristics (number, size, shape, etc.) of the complete set of chromosomes inherent in the cells of a given biological species ( species karyotype ), this organism ( individual karyotype ) or line (clone) of cells. A karyotype is sometimes also called a visual representation of the complete chromosome set (karyogram).
Determination of karyotype
The appearance of chromosomes changes significantly during the cell cycle: during interphase, chromosomes are localized in the nucleus, as a rule, despiralized and difficult to observe, therefore, to determine the karyotype, cells are used in one of the stages of their division - metaphase of mitosis.
Karyotype determination procedure
For the procedure for determining the karyotype, any population of dividing cells can be used; to determine the human karyotype, either mononuclear leukocytes extracted from a blood sample, the division of which is provoked by the addition of mitogens, or cultures of cells that rapidly divide normally (skin fibroblasts, bone marrow cells) are used. The cell culture population is enriched by stopping cell division at the metaphase stage of mitosis by adding colchicine, an alkaloid that blocks the formation of microtubules and the “stretching” of chromosomes to the poles of cell division and thereby preventing the completion of mitosis.
The resulting cells at the metaphase stage are fixed, stained and photographed under a microscope; from the set of resulting photographs, so-called photos are formed. systematic karyotype - a numbered set of pairs of homologous chromosomes (autosomes), images of the chromosomes are oriented vertically with short arms up, they are numbered in descending order of size, a pair of sex chromosomes is placed at the end of the set (see Fig. 1).
Historically, the first non-detailed karyotypes that made it possible to classify according to chromosome morphology were obtained using Romanovsky-Giemsa staining, but further detailing of the chromosome structure in karyotypes became possible with the advent of differential chromosome staining techniques.
Classical and spectral karyotypes.
33. Reproduction of chromosomes in pro- and eukaryotes, relationship with the cell cycle.
Typically, the cell cycle in eukaryotes consists of four time periods: mitosis(M),presynthetic(G1),synthetic(S) And postsynthetic(G2) phases (periods). It is known that the total duration of both the entire cell cycle and its individual phases varies significantly not only in different organisms, but also in cells of different tissues and organs of the same organism.
The universal theory of the cell cycle suggests that the cell as a whole goes through a series of states during the cell cycle ( Hartwell L., 1995). In every condition critical regulatory proteins undergo phosphorylation or dephosphorylation, which determines the transition of these proteins to an active or inactive state, their relationships and/or cellular localization.
Changes in cell states at certain points in the cycle are organized by a special class of protein kinases - cyclin-dependent kinases(Cyclin-dependent kinases - CDK).Cdk form complexes with specific short-lived proteins - cyclins, causing their activation, as well as with other auxiliary proteins.
It is assumed that simplest cell cycle can consist of only two phases - S and M, regulated by the corresponding cdk. This hypothetical cell cycle occurs during early embryogenesis in organisms with large egg cells, such as Xenopus and Drosophila. In these eggs, all components necessary for multiple divisions are presynthesized during oogenesis and stored in the cytoplasm. Therefore, after fertilization, divisions occur extremely quickly, and periods G1 And G2 are missing.
Cell proliferation is controlled by a complex network of extracellular and intracellular events leading to either the initiation and maintenance of the cell cycle or the exit of cells into resting phase.
The central event of the cell cycle is DNA replication.
DNA replication requires the presence of a fairly large set of enzymes and protein factors; packaging of newly synthesized DNA into chromatin also requires de novo synthesis of histones. Expression genes, encoding the listed proteins, is specific to the S-phase.
After replication is complete, when the genetic material is duplicated, the cell enters the postsynthetic state. phase G2, during which preparation for mitosis occurs. As a result of mitosis ( M-phase) the cell divides into two daughter cells. Usually there are two critical transitions between phases - G1/S And G2/M 0.
Based on the cell cycle diagram, we can conclude that the cells would stop at restriction point R V phase G1, if the G1 stage were a biosynthetic reaction much more sensitive to inhibition of overall protein synthesis than any other phase-specific reactions in the cycle.
It was suggested that in order to pass the restriction point R, the concentration of some trigger proteins must exceed a certain threshold level.
According to this model, any conditions that reduce the overall intensity protein synthesis, should delay the accumulation of the threshold concentration of the trigger protein, lengthen the G1 phase and slow down the rate of cell division. Indeed, when cells grow in vitro in the presence of various concentrations of protein synthesis inhibitors, the cell cycle is greatly extended, while the time required to progress through the S, G2 and M phases does not change significantly. The observed prolongation of the G1 phase is consistent with this model, assuming that each trigger protein molecule remains active in the cell for only a few hours. This model also makes it possible to explain the inhibition of cell growth when cell density increases or during starvation; As is known, both of these factors reduce protein synthesis and stop the cell cycle at the most sensitive point of the G1 phase - the R point.
Apparently, the mechanisms that control cell growth in tissue directly affect the overall intensity of protein synthesis in cells; According to this hypothesis, in the absence of specific stimulating factors (and/or in the presence of inhibitory factors), cells will synthesize proteins only at a certain basal level that maintains the status quo. Cm RB protein: role in cell cycle regulation. In this case, the number of proteins with an average renewal rate will be maintained at the same level as in growing cells, and the concentration of unstable proteins (including the trigger protein will decrease in proportion to the decrease in the rate of their synthesis. Under conditions conducive to the acceleration of general protein synthesis , the amount of trigger protein will exceed a threshold level, which will allow cells to pass the restriction point R and begin dividing.
From school biology textbooks, everyone has become familiar with the term chromosome. The concept was proposed by Waldeyer in 1888. It literally translates as painted body. The first object of research was the fruit fly.
General information about animal chromosomes
A chromosome is a structure in the cell nucleus that stores hereditary information. They are formed from a DNA molecule that contains many genes. In other words, a chromosome is a DNA molecule. Its amount varies among different animals. So, for example, a cat has 38, and a cow has 120. Interestingly, earthworms and ants have the smallest numbers. Their number is two chromosomes, and the male of the latter has one.
In higher animals, as well as in humans, the last pair is represented by XY sex chromosomes in males and XX in females. It should be noted that the number of these molecules is constant for all animals, but their number differs in each species. For example, we can consider the content of chromosomes in some organisms: chimpanzees - 48, crayfish - 196, wolves - 78, hare - 48. This is due to the different level of organization of a particular animal.
On a note! Chromosomes are always arranged in pairs. Geneticists claim that these molecules are the elusive and invisible carriers of heredity. Each chromosome contains many genes. Some believe that the more of these molecules, the more developed the animal, and the more complex its body is. In this case, a person should have not 46 chromosomes, but more than any other animal.
How many chromosomes do different animals have?
You need to pay attention! In monkeys, the number of chromosomes is close to that of humans. But the results are different for each species. So, different monkeys have the following number of chromosomes:
- Lemurs have 44-46 DNA molecules in their arsenal;
- Chimpanzees – 48;
- Baboons – 42,
- Monkeys – 54;
- Gibbons – 44;
- Gorillas – 48;
- Orangutan – 48;
- Macaques - 42.
The canine family (carnivorous mammals) has more chromosomes than monkeys.
- So, the wolf has 78,
- the coyote has 78,
- the small fox has 76,
- but the ordinary one has 34.
- The predatory animals lion and tiger have 38 chromosomes.
- The cat's pet has 38, while his dog opponent has almost twice as many - 78.
In mammals that are of economic importance, the number of these molecules is as follows:
- rabbit – 44,
- cow – 60,
- horse – 64,
- pig – 38.
Informative! Hamsters have the largest chromosome sets among animals. They have 92 in their arsenal. Also in this row are hedgehogs. They have 88-90 chromosomes. And kangaroos have the smallest amount of these molecules. Their number is 12. A very interesting fact is that the mammoth has 58 chromosomes. Samples were taken from frozen tissue.
For greater clarity and convenience, data from other animals will be presented in the summary.
Name of animal and number of chromosomes:
| Spotted martens | 12 |
| Kangaroo | 12 |
| Yellow marsupial mouse | 14 |
| Marsupial anteater | 14 |
| Common opossum | 22 |
| Opossum | 22 |
| Mink | 30 |
| American badger | 32 |
| Corsac (steppe fox) | 36 |
| Tibetan fox | 36 |
| Small panda | 36 |
| Cat | 38 |
| a lion | 38 |
| Tiger | 38 |
| Raccoon | 38 |
| Canadian beaver | 40 |
| Hyenas | 40 |
| House mouse | 40 |
| Baboons | 42 |
| Rats | 42 |
| Dolphin | 44 |
| Rabbits | 44 |
| Human | 46 |
| Hare | 48 |
| Gorilla | 48 |
| American fox | 50 |
| striped skunk | 50 |
| Sheep | 54 |
| Elephant (Asian, savannah) | 56 |
| Cow | 60 |
| Domestic goat | 60 |
| Woolly monkey | 62 |
| Donkey | 62 |
| Giraffe | 62 |
| Mule (hybrid of a donkey and a mare) | 63 |
| Chinchilla | 64 |
| Horse | 64 |
| Gray fox | 66 |
| White-tailed deer | 70 |
| Paraguayan fox | 74 |
| Small fox | 76 |
| Wolf (red, ginger, maned) | 78 |
| Dingo | 78 |
| Coyote | 78 |
| Dog | 78 |
| Common jackal | 78 |
| Chicken | 78 |
| Pigeon | 80 |
| Turkey | 82 |
| Ecuadorian hamster | 92 |
| Common lemur | 44-60 |
| Arctic fox | 48-50 |
| Echidna | 63-64 |
| Jerzy | 88-90 |
Number of chromosomes in different animal species
As you can see, each animal has a different number of chromosomes. Even among representatives of the same family, indicators differ. We can look at the example of primates:
- the gorilla has 48,
- the macaque has 42, and the marmoset has 54 chromosomes.
Why this is so remains a mystery.
How many chromosomes do plants have?
Plant name and number of chromosomes: