Chromosome are nucleoprotein structures of eukaryotic cells, in which most of the hereditary information is stored. Due to its ability to self-reproduction, it is chromosome that provide a genetic connection of generations. Chromosomes are formed from a long DNA molecule, which contains a linear group of multiple genes, and all genetic information be about a person, animal, plant, or any other living creature.
The morphology of chromosomes is associated with the level of their spiralization. So, when the chromosome interphase stage is maximally deployed, then with the beginning of chromosome division, they are actively spiralized and shortening. They achieve their maximum shortening and spiralization during the metaphase stage when new structures are forming. This phase is most convenient to study the properties of chromosomes, their morphological characteristics.
History of opening chromosomes
In the middle of the XIX century in the middle of the XIX century, many biologists studying in the structure of plants and animal cells, drew attention to thin threads and the smallest ring-shaped structures in the kernel of some cells. And now the German scientist Walter Fleming applies aniline dyes to treat nuclear cell structures, which is called "officially" opens chromosomes. More precisely, the detected substance was called "chromatid" for its ability to stain, and the term "chromosomes" in everyday life (in 1888) introduced another German scientist - Heinrich Wilder. The word "chromosome" comes from the Greek words "Chroma" - painting and "Somo" - body.
Chromosomal theory of hereditary
Of course, the history of study by chromosomes did not end in their opening, so in 1901-1902, American scientists Wilson and Saton, and independently of each other, drew attention to the similarities in the behavior of chromosome and Mendeleev's heredity factors - genes. As a result, scientists came to the conclusion that the genes are in chromosomes and precisely through them from generation to generation, genetic information is transferred from parents to children.
In 1915-1920, the participation of chromosomes in the transfer of genes was proven in practice in a whole series of experiences made by American scholars and employees of his laboratory. They managed to localize in chromosomes of flies-drosophila several hundred hereditary genes and create genetic maps of chromosomes. Based on this data, a chromosomal theory of heredity was created.
Building chromosomes
The structure of chromosomes will be varied depending on the type, so the metaphase chromosome (formed in the metaphase stage during cell division) consists of two longitudinal threads - chromatide, which are connected at the point of the centromer. Centrome is a section of chromosome, which is responsible for the discrepancy between nursing chromatids in subsidiaries. She divides chromosoma into two parts, called short and long shoulders, it is also responsible for dividing chromosome, since it contains a special substance - the kinetchor, to which the structures of the separation of division are attached.
Here in the picture shows the visual structure of the chromosome: 1. Chromatids, 2. centromer, 3. Short shoulder chromatid, 4. Long shoulder chromatide. At the ends, the chromatids are televomers, special elements that protect chromosomes from damage and prevent the sticking of fragments.
Forms and types of chromosomes
The size of chromosomes of plants and animals differ significantly: from the fraction of the micron to tens of microns. The average length of the metaphase chromosome of a person is in the range from 1.5 to 10 microns. Depending on the type of chromosome, its ability to stain is different. Depending on the location, the centrners distinguish such forms with chromosomes:
- Metic-centered chromosomes for which the middle arrangement of centromeds is characteristic.
- Sublesstrical, for them is characterized by an uneven arrangement of chromatide, when one shoulder is longer, and the second is shorter.
- ACROCENTRIC or ropyoid. They have a centromer located almost at the very end of the chromosome.
Functions chromosomes
The main functions of chromosome, both for animals and plants and in general all living beings - the transfer of hereditary, genetic information from parents to children.
Set of chromosomes
The chromosome value is so large that their number in cells, as well as the features of each chromosome, determine the characteristic feature of a particular biological species. For example, the flies of frosophila in the presence of 8 chromosomes, y - 48, and a chromosomal set of a person is 46 chromosomes.
In nature, there are two main types of chromosomes: single or haploid (contained in germ cells) and double or diploid. The diploid set of chromosomes has a paired structure, that is, the entire totality of chromosomes consists of chromosomal pairs.
Chromosomal set of man
As we have already written above, the cells of the human body contain 46 chromosomes, which are combined into 23 pairs. All together they constitute a chromosomal set of man. The first 22 pairs of human chromosomes (they are called autosomes) are common for both men and women, and only 23 pairs - sex chromosomes - will be varied from different floors, it also defines a person's sexuality. The combination of all pairs of chromosomes is also called a karyotype.
This species has a chromosomal set of man, 22 pairs of double diploid chromosomes contain all of our hereditary information, and the last pair differs, in men, it consists of a pair of conditioner X and Y genital chromosomes, while in women in the presence of two chromosomes H.
All animals are similar to the structure of the chromosomal set, only the number of non-chromosomes each of them has its own.
Genetic diseases associated with chromosomes
Violation in the work of chromosomes, or even their very incorrect amount is the cause of many genetic diseases. For example, Down syndrome appears due to the presence of excess chromosome in a chromosomal human set. And genetic diseases such as daltonism, hemophilia is caused by failures in the work of the existing chromosomes.
Chromosome, video
And in conclusion, an interesting educational video about chromosome.
This article is available in English.
Chromosome - self-reproducing cell kernel structures. Both the prokaryotic and eukaryotic organisms of genes are arranged by groups on separate DNA molecules, which, with the participation of proteins and other macromolecules of cells, are organized in chromosome. Mature magnificent cells (gamets - egg cells, sperm) of multicellular organisms contain one (haploid) set of chromosoma of the body.
After the poles are full sets of chromatids, they are called chromosomes (Chromosomes). Chromosomes are structures in the kernel of eukarot cells, which are spatially and functionally organized DNA in the genome of individuals.
Each DNA molecule is packed in a separate chromosome, and all genetic information stored in chromosomes of one organism is its genome. It should be noted that the chromosomes in the cell change their structure and activity in accordance with the stage of the cell cycle: in mitosis, they are more condensed and transcriptionally inactivated; In the interfax, on the contrary, they are active in terms of RNA synthesis and less condensed.
To form a functional chromosome, the DNA molecule should be capable not only to direct the synthesis of RNA, but also multiplying, transmitted from one cell generation to the next one. For this, three types of specialized nucleotide sequences are needed (they have been identified on Saccharomyces Cerevisiae chromosomes).
1. For normal replication, the DNA molecule requires a specific sequence acting as a dna replication origin (DNA ORIGIN).
2. The second necessary element - centromer - holds two copies of the duplicated chromosome together and attaches any DNA molecule containing this sequence, through the protein complex - the kinetchor to the mitotic spindle (in the process of cell division so that each subsidiary receives one copy.
3. The third necessary element in which each linear chromosome needs is a telomer. Telomer is a special sequence at the end of each chromosome. This simple repeating sequence is periodically extended by a special enzyme, telomerase, and thus compensates for the loss of several DNA telomereal nucleotides, which occurs in each replication cycle. As a result, the linear chromosome turns out to be completely replicated. All elements described above are relatively short (usually less than 1,000 pairs of foundations each). Apparently, similar three types of sequences should work in human chromosomes, but by now only the telomeric sequences of the human chromosome are well characterized.
The diploid (polyploidal) organisms, the cells of which contain one (several) set of chromosome of each of the parents, the same chromosomes were called homologous chromosomes, or homologues. Homologic are the same chromosomes of different organisms of one biological species.
The genes and non-nucleotide sequences enclosed in chromosomes of cell nuclei represent most of the genome of the body.
In addition, the organism genome is formed and extrachromosomal genetic elements, which during the mitotic cycle are reproduced independently of the chromosome of the nuclei. Thus, the mitochondria of mushrooms and mammals contains about 1% of the total DNA, the Sacharomyces Cerevisiae binding yeast - up to 20% of the cell DNA. DNA plants of plants (chloroplasts and mitochondria) ranges from 1 to 10% of the total number of DNA.
The genes included in the individual chromosomes are in the same DNA molecule and form a clutch group, in the absence of recombination together are transferred from parental cells to the subsidiary.
The physiological importance of the distribution of genes on individual chromosomes and the nature of the factors determining the number of chromosomes in the eukaryot genome is not understood. For example, it is impossible to explain the evolutionary mechanisms for the appearance of a large number of chromosomes in specific organisms only by the limitations imposed on the maximum size of DNA molecules that are part of these chromosomes. Thus, the Amphiuma American amphibian genome contains a ~ 30 times more DNA than the human genome, and all DNA is imprisoned only in 28 chromosomes, which is quite comparable to the human karyotype (46 chromosomes). However, even the smallest of these chromosomes is greater than the largest chromosome of man. There are unknown factors that limit the upper limit of the number chromosome in eukaryotes. For example, at the butterfly Lysandra Nivescens diploid set is 380-382 chromosome, and there is no reason to believe that this value is the maximum possible.
Normally, the number of chromosomes in humans is 46. Examples: 46, XX, a healthy woman; 46, XY, healthy man.
Lecture number 3.
Topic: Organization of the flow of genetic information
Plan lectures
1. The structure and functions of the cell nucleus.
2. Chromosome: Structure and classification.
3. Cell and mitotic cycles.
4. Mitosis, Meiosis: Cytological and cytogenetic characteristics, value.
The structure and functions of the cell nucleus
The main genetic information is enclosed in the core of the cells.
Cell kernel (Lat. - nucleus.; Greek. - karyon.) It was described in 1831. Robert Brown. The shape of the nucleus depends on the shape and functions of the cell. The sizes of cores vary depending on the metabolic activity of cells.
An interphase core sheath (caryolamma) Consists of outer and internal elementary membranes. Between them is perinuclear space. In the membranes there are holes - pores.Between the edges of the nuclear pore are protein molecules that form pore complexes. The pore hole is closed with a thin film. With active metabolic processes in the cell, most pores are open. Through them there is a stream of substances - from the cytoplasm in the kernel and back. Number of pores in one nucleus
Fig.The scheme of the structure of the cell core
1 and 2 - the outer and inner membrane of the nuclear shell, 3
- Nuclear time, 4 - Yadryshko, 5 - Chromatin, 6 - nuclear juice
reaches 3-4 thousand. The outer nuclear membrane is connected to the channels of the endoplasmic network. It usually arranges ribosomes. The proteins of the inner surface of the nuclear shell form nuclear plate. It supports the constant shape of the nucleus, chromosomes are attached to it.
Nuclear Juice - Kariolimf, colloidal solution in the state of the gel, which contains proteins, lipids, carbohydrates, RNA, nucleotides, enzymes. Nadryshko - non-permanent kernel component. It disappears at the beginning of cell division and is restored at the end of it. Chemical composition of nucleolus: protein (~ 90%), RNA (~ 6%), lipids, enzymes. The nuclei are formed in the field of secondary pigeons of satellite chromosomes. The function of the nucleus: assembly of subunit ribosomes.
H. roman The nuclei is the interphase chromosomes. They contain DNA, proteins-histones and RNA in a ratio of 1: 1.3: 0.2. DNA in connection with protein forms deoxyribonucleoprotein (DNP). With mitotic division of the NDP kernel spiral and forms chromosome.
Functions of the cell kernel:
1) keeps the hereditary information of the cell;
2) participates in division (reproduction) cells;
3) regulates the metabolic processes in the cell.
Chromosome: Structure and Classification
Chromosomes (Greek - - chromo. - color, soma. - Body) is spiralized chromatin. Their length is 0.2 - 5.0 μm, diameter 0.2 - 2 microns.
Fig.Types chromosomes
Methazna chromosome Consists of two chromatidwhich are connected centromer (primary drawing). She divides chromosomes for two shoulder. Separate chromosomes have secondary drying. The site that they separate is called satellite, and such chromosomes - satellite. End plots chromosomes are called telomeres. Each chromatide includes one continuous DNA molecule in a combination with Histon proteins. Intensively staining sections with chromosomes are plots of strong spiralization ( heterochromatin). Lonely sections - sections of weak spiralization ( eukhromatin).
Types of chromosomes are isolated by the location of centromers (Fig.).
1. Metic centers chromosomes - Centrome is located in the middle, and the shoulders have the same length. The shoulder section near the centrometers is called proximal, opposite - distal.
2. Sublesstritic chromosomes - The centride is shifted from the center and shoulders have different lengths.
3. Acrocentric chromosomes - The centromer is strongly shifted from the center and one shoulder is very short, the second shoulder is very long.
In the cells of the salivary glands of insects (flies of drosophyl) there are gigantic, polluted chromosomes (Multi-grated chromosomes).
For chromosomes of all organisms there are 4 rules:
1. Rule of constancy number chromosome. Normally, the organisms of certain species have a constant, characteristic of the type of chromosome. For example: Human 46, in a dog 78, in Fly Drozophila 8.
2. Pawn chromosomes. In the diploid set in the norm, each chromosome has a pair chromosome - the same in shape and largest.
3. Individuality chromosomes. Chromosome of different pairs differ in shape, structure and magnitude.
4. Continuity chromosomes. When doubling the genetic material of the chromosome is formed from chromosome.
A set of chromosome of a somatic cell characteristic of the body of this species is called karyotype.
Classification of chromosomes are carried out according to different features.
1. Chromosomes, the same in the cells of the male and female organisms, are called autosomas. In a person in the karyotype 22 pairs of autos. Chromosomes, various in the cells of the male and female organisms are called heterochromosomes, or sex chromosomes. In a man, it is X and Y chromosome, in women - X and H.
2. The location of chromosomes in a decreasing value is called idiogram. This is a systematized karyotype. Chromosome are placed in pairs (homologous chromosomes). The first pair is the largest, 22th pair - the small and 23rd pair - sex chromosomes.
3. In 1960. Denver classification of chromosomes was proposed. It is built on the basis of their shape, sizes, positions of centromeres, the presence of secondary drawings and satellites. An important indicator in this classification is centering Index (Qi). This is the ratio of the short shoulder length of the chromosome to its entire length, expressed in percent. All chromosomes are divided into 7 groups. Groups are denoted by Latin letters from A to G.
Group A. Includes 1 - 3 pairs of chromosomes. These are large meticenter and submetrical chromosomes. They are 38-49%.
Group B.. The 4th and 5th pairs are large meticenter chromosomes. Qi 24-30%.
Group S.. Couple chromosomes 6 - 12: medium, submetrical. Qi 27-35%. This group includes x-chromosome.
Group D.. 13 - 15th pairs of chromosomes. Chromosome acrocentric. Qi about 15%.
E. Group. Couple chromosomes 16 - 18. Comparatively short, meticenter or submetrical. Qi 26-40%.
Group F.. 19 - 20th Couples. Short, submetrical chromosomes. Qi 36-46%.
Group G.. 21-22 pages. Small, acrocentric chromosomes. Qi 13-33%. This group includes y-chromosome.
4. Paris classification of a man chromosoma was created in 1971. With this classification, it is possible to determine the localization of genes in a certain pair of chromosomes. Using special coloring methods, each chromosome detects the characteristic procedure for the alternation of dark and light strips (segments). Segments are denoted by the names of the methods that detect them: q - segments - after staining with acryoine-iprite; G - segments - painting by the gymnus dye; R - segments - staining after thermal denaturation and others. The short shoulder chromosome is denoted by the letter P, the long - letter Q. Each shoulder chromosomes are divided into areas and denote numbers from centromers to the Telomer. The strips inside the areas are numbered in order from the centromere. For example, the arrangement of the Esterase D - 13P14 gene is the fourth strip of the first district of the 13th chromosome.
Function chromosomes: storage, reproduction and transmission of genetic information in the reproduction of cells and organisms.
Similar information.
2. Chromosomal cell set
An important role in the cell cycle belongs to chromosomes. Chromosomes - carriers of hereditary cell information and the body contained in the kernel. They not only regulate all metabolic processes in the cell, but also ensure the transfer of hereditary information from one generation of cells and organisms to another. The number of chromosomes corresponds to the number of DNA molecules in the cell. An increase in the number of many organoids does not require accurate control. All cell content in division is distributed more or less evenly between two daughter cells. The exceptions are chromosomes and DNA molecules: they must double and accurately distribute between the newly formed cells.
Building chromosomes
The study of chromosomes of eukaryotic cells showed that they consist of DNA molecules and protein. The DNA complex with protein is called chromatin. The prokaryotic cell contains only one DNA annular molecule that is not associated with proteins. Therefore, strictly speaking, it cannot be called chromosome. This is a nucleoid.
If it was possible to stretch the DNA thread of each chromosome, then its length would significantly exceed the size of the kernel. An important role in the packaging of giant DNA molecules is played by nuclear proteins - histones. Recent studies of the structure of chromosomes have shown that each DNA molecule is connected to groups of nuclear proteins, forming many repetitive structures - nucleosom (Fig. 2). Nucleosome are structural units of chromatin, they are tightly packed together and form a single structure in the form of a spiral with a thickness of 36 nm.
Fig. 2. The structure of the interphase chromosome: A - electronic photography of chromatin yarns; B - nucleosome, consisting of proteins - histones, around which spiralically swirling DNA molecule
Most chromosomes in the interfase are stretched in the form of threads and contain a large number of desponde plots, which makes them practically invisible to the usual light microscope. As mentioned above, before dividing the cells of the DNA molecule, each chromosome consists of two DNA molecules that are spiralized, connected with proteins and acquire clear forms. Two daughter DNA molecules are packaged apart and form nursing chromatids. Nursing chromatids are held together by the centromer and form one chromosome. Centrometer - This is a section of the clutch of two nursing chromatids, controlling the movement of chromosomes to the cell poles during division. This part of chromosomes are attached threads of the separation of division.
Separate chromosomes differ only in the period of cell division when they are as tightly packed as much as possible, they are well stained and visible in the light microscope. At this time, you can define their number in the cell, study a general view. Each chromosome stand out shoulders chromosomes and centromer. Depending on the situation, the centrners distinguish three types of chromosomes - topboard, Divorced and obligible (Fig. 3).
Fig. 3. The structure of the chromosome. A - scheme of the chromosome structure: 1 - centromer; 2 - shoulders of chromosome; 3 - nursing chromatids; 4 - DNA molecules; 5 - protein components; B - Types of chromosomes: 1 - equally flying; 2 - Dipleless; 3 - Sieleburst
Chromosomal cell set
Cells of each body contain a certain set of chromosomes called karyotype. For each type of organisms, its karyotype is characteristic. Chromosome of each karyotype differ in the form - the value and a set of genetic information.
The karyotype of man, for example, is 46 chromosomes, fruit flock of drosophila - 8 chromosomes, one of the cultural types of wheat - 28. The chromosomal set is strictly specific for each species.
Studies of the karyotype of various organisms showed that in cells there may be a single and double chromosome set. Double, or diploid(from Greek. diploos. - Double I. eidos. - view), a set of chromosomes is characterized by the presence of paired chromosomes that are the same in size, form and nature of hereditary information. Paired chromosomes are called homologous (from Greek. homois - Same, similar). For example, all the somatic human cells contain 23 pairs of chromosomes, i.e. 46 chromosomes are represented as 23 pairs. Drosophila 8 chromosomes form 4 pairs. Paired homologous chromosomes outwardly very similar. Their centromers are in the same places, and the genes are located in the same sequence.
Fig. 4. Sets of chromosomes of cells: a - plants of the scraples, b - mosquito, in - drosophila, g - humans. A set of chromosomes in the genital cell Drozophila Gaploid
In some cells or organisms there may be a single set of chromosomes, which is called haploid (from Greek. haploos. - Single, simple and eidos. - view). The paired chromosomes in this case are not available, i.e. there is no homologous chromosomes in the cell. For example, in the cells of the lower plants - algae set chromosomes, the Haploid, whereas of the highest plants and animals a set of chromosomes diploid. However, in the genital cells of all organisms there is always only a hollow-shaped chromosome set.
The chromosomal set of cells of each organism and the species in general is strictly specific and is its main characteristic. Chromosomal set is made to denote Latin letter n. The diploid set is respectively designated 2n, and haploid - n.The number of DNA molecules is indicated by the letter c. At the beginning of the interphase, the number of DNA molecules corresponds to the number of chromosomes and in the diploid cell is equal to 2c. Before the start of division, the number of DNA doubles and equals 4C.
Questions for self-control
1. What structure does an interphase chromosome have?
2. Why is it impossible to see the chromosomes in the microscope in the interfase?
3. How determines the number and appearance of chromosomes?
4. Name the main parts of the chromosome.
5. From how many DNA molecules is the chromosome in the pre-interphalase pre-period and the cell division?
6. Due to what process changes the number of DNA molecules in the cell?
7. What chromosomes are called homologous?
8. For a set of chromosome, Drozophils determine the equal departure, diverse and single-light chromosomes.
9. What is the diploid and haploid kits chromosome? How are they designated?
From the book health of your dog Author Baranov AnatolyA set of medicines in the syringe with a set of medicines in the syringe should be extremely attentive. Once again it is necessary to read the appointment of a doctor, to verify with inscriptions on the ampoule, make sure that the transparency of the solution and the absence of flakes in it. Maply can be sprinkled with a pailer in
From the book the newest book of facts. Volume 1 [Astronomy and Astrophysics. Geography and other earth sciences. Biology and medicine] Author From book Tests on biology. 6th grade The author of Benggy ElenaCellular structure of organisms Cell structure. Devices for studying the structure of the cell 1. Select one of the most correct answer. The clotch is: a. The smallest particle of the whole lived. The smallest particle of live plants. Part of plants. Artificially created unit for
From the book Biology [full guide to prepare for the exam] Author Lerner Georgy Isaakovich From book flight from loneliness Author Panov Evgeny Nikolaevich From the book the newest book of facts. Volume 1. Astronomy and astrophysics. Geography and other earth sciences. Biology and medicine Author Kondrashov Anatoly PavlovichCells - Security Talking about the progressive role that the first sketches of the cell theory played, it is impossible not to make a reservation that I created by it the image of "sovereign" cells only to a limited extent to the organisms of higher animals, although the cells are sometimes leading
From the book, who leads? [Biology of human behavior and other animals] Author Zhukov. Dmitry AnatolyevichCell-collectivist cells and single cells are based on close cooperation of cells that are part of a multicellular organism lie at least two major reasons. First, each separately taken cell, being herself by itself for a rarity skillful and executive
From the book of the problem of medical starvation. Clinical and experimental studies [all four parts] Author Anokhin Peter KuzmichCan a crime chromosome set to serve as an excuse for the crime committed them? One of the violations of sex chromosomes is an extra y-chromosome in a karyotype (a set of signs of chromosomes characteristic of the body cells of a body of a particular type)
From the book, the power of genes [is beautiful as Monroe, smart as Einstein] Author Hungstshleger MarcusThe chromosomal phase of floor formation floor begins to be determined during fertilization. In the nuclei of human cells, one pair of chromosomes are different in men and women. In women, this pair under the microscope is similar to two letters X, and men are in the letters XY. Accordingly, these chromosomes and
From the book genes and the development of the body Author Neathah Alexander AlexandrovichOn the action of complete long-term alimentary starvation on the chromosomal apparatus of peripheral blood lymphocytes K. N. Greenberg, Yu, L. Shapiro, E. A. Kirilova, R. S. Kushnir (Moscow) Completely alimentary starvation is successfully applied in the treatment of some mental and
From the book the evolution of man. Book 1. Monkeys, bones and genes Author Markov Alexander VladimirovichThe same set of genes from different people is good, if it makes no sense to track some disease throughout the family tree - what then? The scientifically based answer to the question is what is related to genes, gives the result of an amazing nature experiment. Human -
From the book Secrets of Humanity Man Author Afonkin Sergey Yuryevich2. Blood cells The blood formation system is more complicated by other systems with a constant update of differentiated cells. In this case, there is no such simple spatial separation of stem cells, differentiable cells and cells reached the terminal
From the book the reproduction of organisms Author Petrosova Renata ArmenaknaMitochondrial Eva and Khromosomal Adam in African Eden Comparative Analysis of Mitochondrial DNA (MTDNA) and Y-chromosomes of modern people showed that all modern humanity comes from a small population who lived in East Africa 160-200 thousand years.
From the book of the authorImmortal cells Birth and death are often perceived by us as two sides of the same medal. One phenomenon is supposedly inseparable from the other. The emergence of the light inevitably entails aging and death. Meanwhile, this is not quite so. Live cell like a peculiar molecular
From the book of the authorThe repair kit is clear that if the cells had no protection against such DNA disorders, soon many genes would be irreversibly damaged that the body would inevitably lead to a complete disaster. It is not surprising, therefore, that any cells regularly and constantly do
From the book of the author3. Cell division The ability to divide is the most important property of the cell. As a result of division from one cell, two new ones occur. One of the main properties of life is self-reproduction - manifests itself at the cellular level. The most common way to divide
Chromosomes (Greek Chroma Color, Color + Soma Body) - The main structural-functional elements of the cell nucleus containing genes located in linear manner and providing storage, reproduction of genetic information, as well as the initial stages of its implementation in signs; Change their linear structure in the cell cycle. The term "chromosomes" is proposed by Valteer (Waldeyer) in 1888 due to a row-shaped and intensive staining of these elements with the main dyes during cell division.
The term "chromosome" in its full meaning is applicable to the corresponding nuclear structures of cells of multicellular eukaryotic organisms (see). In the kernel of such cells, chromosomes are always several, they constitute a chromosomal set (see). In the somatic cells of the chromosomes of the guy, as they occur from two parents (diploid set of chromosomes), in mature genital cells contain a single (haploid) chromosome set. Each biological species is characterized by a constant number, dimensions and other morphological signs of chromosomes (see karyotype). In all-choice organisms, the chromosomal set includes two chromosomes that carry genes that determine the floor of the individual (see gene, gender), which are called sexual, or gonomas, as opposed to all other, called autosomas. A person has a pair of sex chromosomes: in women from two X chromosomes (XX set), and in men from X and Y-chromosome (XY set). Therefore, in mature genital cells - govetakes, women contain only X-chromosome, while men have half of the spermatozoa contains a X-chromosome, and the other - y-chromosome.
History
The first observations of chromosomes in the core of the cell, made in the 70s of the 19th century I. D. Chistyakov, O. Gerty, Strasburger (E. Strasburger), marked the beginning of the cytological direction in the study of chromosomes. Until the beginning of the 20th century, this direction was the only one. The use of a light microscope made it possible to obtain information on the behavior of chromosomes in mitotic and meiotic divisions (see Meiosis, Mitosis), facts about the constancy of the chromosome number from this species, special types of chromosomes. In the 20s of the 20th year of the 20th century, a comparative morphological study of chromosomes was obtained preferential development in different types of organisms, including a person, in order to clarify the general principles of their organization, features of individual chromosomes and changes in their evolution. In the study of this problem, domestic scientists S. G. Navashin, G. A. Levitsky, L. N. Delone, P. I. Zhivago, A. G. Andres, M. S. Navashin, A. A. P Rocofeeva-Belgovskaya, as well as foreign - Heitz (E. Heitz), Darlington (S. D. Darlington), etc. From the 50s, an electronic microscope was used to study chromosomes. The study of morphological changes in chromosomes in the process of their genetic functioning began. In 1956, Tio (H. J. Tjio) and Levan (A. Levan) finally established the number of chromosomes in a person equal to 46, described their morphological signs in mitosis metaphase. Significant progress in the study of chromosomes was achieved in the 70s after the development of various methods of their coloring, which allowed to identify the heterogeneity of the structure of chromosomes in length in the meta phase of cell division.
Comparison of the behavior of chromosomes in meiotic division with the patterns of inheritance of signs (see Mendel law) laid the beginning of cytogenetic research. At the end of the 19th - early 20th century Setton (W. Sutton), Bovteri (TH. Boveri), Wilson (E. V. Wilson) were laid the foundations of the chromosomal theory of heredity (see), according to which the genes are localized in chromosomes and the behavior of the latter The ripening of heamers and their merger at the time of fertilization explains the laws of transmission of signs in generations. The theory received a final substantiation in cytogenetic experiments conducted on Drozophile (see) T. Morgan and his students who have proven that each chromosome is a group of genes captured inherited and located in a linear manner that gene recombination is carried out in MEIZE (see recombination ) Homologous (identical) chromosomes.
The study of the biochemical nature of chromosomes, begun in the 30s-40th years of the 20th century, was originally based on cytochemical qualitative and quantitative determination of the content of DNA, RNA and proteins in the nucleus. Since the 50s, photo and spectrometry (see spectrophotometry), X-ray-based analysis (see) and other physicochemical methods began to be used for these purposes.
Physical and chemical chromosome
The physico-chemical nature of chromosomes depends on the complexity of the organization of the biological species. Eukarot chromosome consists of a deoxyribonucleic acid molecule (see), histone and nonregistone proteins (see Histons), as well as ribonucleic acid (see). The main chemical component of chromosomes entering into the structure of its molecule genetic information is DNA. In natural conditions, in certain sections of DNA chromosome, it may be free from structural proteins, but it mainly exists in the form of a complex with histones, both in the interfax and in metaphase, the weight ratio of the DNA / Histon is one. The content of acidic proteins in chromosomes varies depending on their activity and the degree of condensation in the cell cycle. In chromatin (see) the interphase nucleus and at any stage of mitotic condensation, DNA exists in a complex with histones, and the interaction of these molecules creates elementary structural particles of chromatin - nucleosome. In the nucleosome, its central part is 8 histone molecules of four types (2 molecules from each type). These are histones H2A, H2B, NZ and H4, interacting with each other, apparently, the C-terminal areas of molecules. N-terminal areas of histone molecules interact with a DNA molecule in such a way that the latter turns out to be coated on the histone ease, making two turns on one side of it and one to another. One nucleosome accounts for about 140 pairs of DNA bases. Between adjacent nucleosums there is a varies on the length of the length of the DNA (10-70 pairs of bases). When it is straightened, DNA takes the type of thread with beads. If the segment is in the folded state, the nucleosomes are closely adjacent to each other, forming a fibril with a diameter of 10 nm. The structure of nucleosomal particles is the principle of organizing the chromatin (see) both in the interphase and metaphase chromosome.
Individually distinguishable chromosomes are formed by the time of cell division, mitosis or meiosis, as a result of progressively increasing condensation by chromosomes. In the protopase of mitotic division of chromosomes, they are visible in a light microscope in the form of long and twisted threads, so individual chromosomes throughout indistinguishable. In the protopase of the first meiotic division of chromosomes, complex specific morphological transformations are undergoing mainly with the conjugation of homologous chromosomes (see the conjugation of chromosomes) and genetic recombination (exchanging sites) between them. In Patchithee (when conjugation ends), the alternation of the chromomer along the length of chromosomes is especially significant, and the chromomeric pattern is specific for each chromosome and changes as the condensation. Many chromosome in oogenesis and y-chromosome in spermatogenesis have high transcriptional activity. In some types of organisms, such chromosomes were called "tube brushes". They consist of an axis constructed from chromomer and interchromomeric sites, and numerous lateral loops - decondes of chromomer in a state of genetic functioning (transcription).
In the chromosome cell division metaphase, they have the smallest length and are easy to investigate, therefore the description of individual chromosomes, like all their sets in the cell, is given in relation to their state in this phase. The size of the metaphase chromosomes in the same type of organisms is highly different: chromosomes with dimensions in the shares of the micron have a point look, with a length of more than 1 microns, they look like rod-shaped bodies. It is usually split in length of formation consisting of two nursing chromatids (Fig. 2, 3), since chromosome metaphase is reduced.
Individual chromosomes of the set differ in length in length and other morphological features. The methods used until the 70s ensured uniform staining of the chromosome at its length. Nevertheless, such a chromosome as a mandatory element of the structure has a primary drawing - a plot where both chromatids are narrowed, apparently not separating one from the other, and poorly stained. This chromosome area is called centromer, it contains a specialized structure - a kinetchor, which is involved in the formation of the threads of the chromosome filament. According to the ratio of the size of the chromosome chromosomes lying on both sides, the chromosome shoulders are divided into three types: meticenteric (with a medianized suspension), submetrical (hauling is shifted from the middle), acrocentric (centromer is located close to the end of the chromosome, Fig. 3). A person has all three types of chromosomes. Chromosome ends are called telomeres. The length of chromosomes with one degree or another consistency may not have a relationship with the centromere, the so-called secondary tugs. If they are located close to the telomere, separated by a hawk distal sector of chromosomes are called a satellite, and a satellite bleeding (Fig. 2). In humans, ten with a secondary hawk chromosome, they are all acrocentric, satellites are localized in a short shoulder. Some secondary bleeds contain ribosomal genes and are called exercise-forming, since due to their functioning in RNA products in the interphase kernel, nucleolus is formed (see). Other secondary tugs are formed by heterochromatic areas of chromosomes; A person from such a tug has the most pronounced aboutcentro-sinks in 1, 9 and 16 chromosomes.
The initial method of using the gyms dye and other chromosomal dyes gave a uniform painting along the entire length of the chromosome. Since the beginning of the 70s, a number of coloring methods and processing of metaphase chromosomes have been developed, which allowed to detect differentiation (division into light and dark bands) of the linear structure of each chromosome along its entire length: Q-coloring (q - from English Quinacrine Acryin), obtained from using acrycine, acryciniprite and other fluorochromes; G-painting (G - from the Giemsa surname), obtained by a gym dye (see Romanovsky - GIMZ methods) after incubation of chromosomes in special conditions; R-coloring (R - from English Reverse Reverse; chromosomes are painted back G-color). The chromosome body turns out to be divided into segments of different intensity of staining or fluorescence. The number, position and size of such segments are specific for each chromosome, so any chromosomal set can be identified. Other methods allow differentially painting the individual specific areas of chromosomes. It is possible to selectively staining with the gimbal of the heterochromatic areas of chromosome (C-color; C - from the centromere of a centromer), located next to the centromer - C-segments (Fig. 4). The human segments have found in the near centromerous area of \u200b\u200ball outosomes and the long shoulder y -chromosomes. The heterochromatic areas vary largest in different individuals, caused by chromosome polymorphism (see chromosomal polymorphism). Specific coloring makes it possible to reveal in metaphase chromosomes functioning nuclei-forming areas in the Interfase, as well as the kinetokhory.
On the electronic microscopic level, the main ultrastructure unit of an interphase chromatin with translucent electron microscopy (see) is a diameter of 20-30 nm. The density of the packing of the threads is different in the plots of dense and diffuse chromatin.
The metaphase chromosome on a cut in a translucent electron microscope seems to be uniformly filled with fibrils 20-30 nm in the diameter, which, depending on the cross section plane, have a view of rounded, oval or elongated formations. In the proofased and bondage in chromosome, thicker threads can be detected (up to 300 nm). At electron microscopy, the surface of the metaphase chromosome is represented by chaotic laid numerous fibrils of different diameters, visible, as a rule, on a short segment (Fig. 5). Threads with a diameter of 30-60 nm prevail.
The variability of chromosomes in ontogenesis and evolution
The constancy of the chromosome number in the chromosomal set and the structure of each chromosome is the indispensable condition for normal development in ontogenesis (see) and the preservation of biol. species. During the life of the body, changes can occur by the number of individual chromosomes and even their haploid sets (genomic mutations) or the structure of chromosomes (chromosomal mutations). Unusual embodiments of chromosomes that determine the uniqueness of the chromosomal set of an individual are used as genetic markers (marker chromosomes). Genomic and chromosomal mutations play an important role in the evolution of biol. species. The data obtained in the study of chromosomes make a great contribution to the systematics of species (cariostematics). In animals, one of the main mechanisms of evolution variability is the change in the number and structure of individual chromosomes. The change in the content of heterochromatin in individual or several chromosomes is also important. A comparative study of human chromosome and modern human-like monkeys made it possible on the basis of similarity and differences with individual chromosomes to establish the degree of phylogenetic kinship of these species and simulate the karyotype of their common nearest ancestor.
Bockov N. P., Zakharov A. F. and Ivanov V. I. Medical Genetics, M., 1984; Darlington S. D. and La Court L. F. Chromosome, work methods, per. from English, M., 1980, bibliogr.; Zakharov A. F. Chromosome of a person (problems of a linear organization;, M., 1977, Bibliogr.; Zakharov A. F. and others. Human chromosomes, Atlas, M., 1982; Kikanadze I. I. Functional organization Chromosome, L. , 1972, Bibliogr.; Basics of human cytogenetics, ed. A. A. Prokofyeva-Belgovskaya, M., 1969: Swonzo N K., Merez T. and Yang W. Citogenetics, Per. From English, M., 1969 ; Cell Biology, A Comprehensive Treatise, ED. By L. Goldstein a. Dm Prescott, p. 267, NY AO, 1979; Seuanez H. N, The Phylogeny of Human Chromosomes, v. 2, B. AO 1979; Sharm A AK a. Sharma A. Chromosome Techniques, L. Ao, 1980; Thermane. Human Chromosomes, NY AO, 1980.
A. F. Zakharov.