Crafts

The chromosomes are rod-shaped bodies located in. Functions and structural features of chromosomes. The number of chromosomes in various organisms

The chromosome set of a person carries not only hereditary characteristics, as it is written in any textbook, but also karmic debts, which can manifest as hereditary diseases, if a person has not managed to change his erroneous perception of reality by the time they are presented for payment, thereby paying off another debt. In addition, a person could distort chromosomes not only by mistakes in his perception of the world, but also by improper diet, lifestyle, staying or working in harmful places, etc. All these factors additionally distort a person's chromosomes, which is easy to see if you periodically undergo state studies chromosomes, for example, on computer diagnostics Oberon. From the same diagnosis, it is clear that with healing, the state of a person's chromosome set improves. Moreover, the restoration of chromosomes and only partial occurs much later than the restoration of the health of an organ or system of a person if a person was healed without working out the root causes. This means that the first to take on the "blow of fate" is the human chromosome, which then manifests itself at the cellular level, and then in the form of a disease.

So, the accumulated "wealth" of errors is fixed in a person at the level of his chromosomes. Distortions in chromosomes close or distort the superpowers of a person and create illusion of fear since distort energy and information, cause an illusory perception of oneself, people and the world around them.

Large distortions in human chromosomes are the root cause of pride, which arises due to the illusory perception of oneself, starting at 12% distortion. Large distortions of the chromosome set are usually inherent in sorcerers and a diverse audience practicing magic (because their energy is low), NLP, Reiki, hypnosis, dianetics, cosmoenergetics, "channels". Such professionals themselves constantly have to use it, because otherwise, the burden of accumulated karma due to the use of harmful methods of pushing problems into the future can crush, the same can be said about unreasonable patients who agree to use such methods.

The average amount of chromosomal distortion in humans is 8%.

Each pair of chromosomes is responsible for its own sphere of health and life. I will cite the data for the 5th, 8th, 17th and 22nd, since it is in them that the main distortions (85% of 100%) are contained in those who will be present at the session on April 19.

The 5th pair of chromosomes is responsible for childbirth, gender relations, the transmission of generic energies, including karmic retributions for negative generic karma (ORK).

The 8th pair is responsible for immunity, cleansing of toxins and toxins, the lymphatic system, the system of defecation and secretions (including sweat glands), urinary, kidneys, liver, spleen, small and large intestines.

The 17th couple is responsible for the production of hormones in the body, including endorphins, the thyroid gland, the pituitary gland, and the entire endocrine system.

The 22nd pair is responsible for the musculoskeletal system and movement control (vestibular apparatus, middle ear and impaired coordination), the production of lactic acid (fatigue), and physical endurance of the body.

Here are some examples:

- Athletes with distortions in the 22nd pair of chromosomes will never be able to achieve significant sporting achievements. More precisely, the magnitude of athletic performance is inversely proportional to the distortions in the 22nd pair of chromosomes.

- A dancer will never become outstanding if she has distortions in the 5th and 22nd pairs of chromosomes.

Distortions in chromosomes are one of the main causes of the appearance of altered cells.

Sometimes they give us amazing surprises. For example, do you know what chromosomes are and how they affect?

We propose to understand this issue in order to dot the i's once and for all.

Looking at family photos, you might have noticed that members of the same kinship are similar to each other: children - like parents, parents - like grandparents. This similarity is passed down from generation to generation through amazing mechanisms.

All living organisms, from unicellular to African elephants, have chromosomes in the nucleus of the cell - thin long filaments that can only be seen under an electron microscope.

Chromosomes (ancient Greek χρῶμα - color and σῶμα - body) are nucleoprotein structures in the cell nucleus, in which most of the hereditary information (genes) is concentrated. They are designed to store this information, its implementation and transmission.

How many chromosomes does a person have

At the end of the 19th century, scientists found out that the number of chromosomes in different species is not the same.

For example, peas have 14 chromosomes, have 42, and a person has 46 (that is, 23 pairs)... Hence, it is tempting to conclude that the more there are, the more complex the creature possessing them. However, in reality, this is not at all the case.

Of the 23 pairs of human chromosomes, 22 are autosomes and one pair are gonosomes (sex chromosomes). Sexual differences have morphological and structural (gene composition) differences.

In the female body, a pair of gonosomes contains two X-chromosomes (XX-pair), and in the male, one X- and one Y-chromosome (XY-pair).

The sex of the unborn child depends on the composition of the chromosomes of the twenty-third pair (XX or XY). This is determined by fertilization and fusion of the female and male reproductive cells.

This fact may seem strange, but in terms of the number of chromosomes, humans are inferior to many animals. For example, some unfortunate goat has 60 chromosomes, and a snail has 80.

Chromosomes consist of a protein and a DNA molecule (deoxyribonucleic acid), similar to a double helix. Each cell contains about 2 meters of DNA, and in total, the cells of our body contain about 100 billion km of DNA.

An interesting fact is that in the presence of an extra chromosome or in the absence of at least one of the 46, a mutation and serious deviations in development (Down's disease, etc.) are observed in a person.

CHROMOSOMES(Greek chroma color, color + soma body) - the main structural and functional elements of the cell nucleus, containing genes arranged in a linear order 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” was proposed by W. Waldeyer in 1888 because of the rod-shaped form and intense staining of these elements with basic 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 nucleus of such cells there are always several chromosomes, they make up a chromosome set (see). In somatic cells, chromosomes are paired, since they come from two parental ones (diploid set of chromosomes), mature germ cells contain a single (haploid) set of chromosomes. Each biological species is characterized by a constant number, size and other morphological characteristics of chromosomes (see Karyotype). In heterosexual organisms, the chromosome set includes two chromosomes carrying genes that determine the sex of an individual (see Gene, Gender), which are called sexual, or gonosomes, as opposed to all others, called autosomes. In humans, a pair of sex chromosomes is composed: in women, from two X chromosomes (XX set), and in men, from X and Y chromosomes (XY set). Therefore, in mature germ cells - gametes, women contain only the X chromosome, while in men half of the spermatozoa contains the X chromosome, and the other contains the Y chromosome.

Story

The first observations of chromosomes in the cell nucleus, carried out in the 70s of the 19th century by ID Chistyakov, O. Hertwig, E. Strasburger, laid the foundation for 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 about the behavior of chromosomes in mitotic and meiotic divisions (see Meiosis, Mitosis), facts about the constancy of the number of chromosomes in a given species, and special types of chromosomes. In the 20-40s of the 20th century, a comparative morphological study of chromosomes in different types of organisms, including humans, was predominantly developed in order to clarify the general principles of their organization, the characteristics of individual chromosomes and their changes in the process of evolution. Russian scientists S.G. Navashin, G.A.Levitsky, L.N. Delone, P.I. Zhivago, A.G. Andres, M.S. Navashin, A.A. rokof'eva-Belgovskaya, as well as foreign ones - E. Heitz, Darlington (S. D. Darlington), etc. Since the 50s, an electron microscope has been used to study chromosomes. The study of morphological changes in chromosomes in the process of their genetic functioning began. In 1956, H. J. Tjio and A. Levan finally established the number of chromosomes in humans, equal to 46, described their morphological features in the metaphase of mitosis. Significant progress in the study of chromosomes was achieved in the 70s after the development of various methods for their staining, which made it possible to reveal the heterogeneity of the structure of chromosomes along the length in the meta phase of cell division.

Comparison of the behavior of chromosomes in meiotic division with the patterns of inheritance of characters (see Mendel's laws) laid the foundation for cytogenetic studies. In the late 19th - early 20th century Setton (W. Sutton), Boveri (Th. Boveri), Wilson (E.V. Wilson) laid the foundations of the chromosomal theory of heredity (see), according to which genes are localized in chromosomes and the behavior of the latter during the maturation of gametes and their fusion at the time of fertilization explains the laws of transmission of characters in generations. The theory was finally substantiated in cytogenetic experiments carried out on Drosophila (see) T. Morgan and his students, who proved that each chromosome is a group of genes linked inherited and arranged in a linear order, that gene recombination is carried out in meiosis (see Recombination ) homologous (identical) chromosomes.

The study of the biochemical nature of chromosomes, begun in the 30s-40s of the 20th century, was originally based on the 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 structural analysis (see) and other physicochemical methods have been used for these purposes.

Physicochemical nature of chromosomes

The physicochemical nature of chromosomes depends on the complexity of the organization biological species... The eukaryotic chromosome consists of a molecule of deoxyribonucleic acid (see), histone and non-histone proteins (see Histones), as well as ribonucleic acid (see). The main chemical component of the chromosome, which contains genetic information in the structure of its molecule, is DNA. Under natural conditions, in individual parts of the chromosome, DNA can be free of structural proteins, but basically it exists in the form of a complex with histones, and both in the interphase and in the metaphase, the weight ratio of DNA / histone is unity. The content of acidic proteins in chromosomes varies depending on their activity and the degree of condensation in the cell cycle. In the chromatin (see) of the interphase nucleus and at any stage of mitotic condensation, DNA exists in a complex with histones, and the interaction of these molecules creates the elementary structural particles of chromatin - nucleosomes. In the nucleosome, its central part is made up of 8 histone molecules of four types (2 molecules from each type). These are histones Н2А, Н2В, НЗ and Н4, interacting with each other, apparently, with the C-terminal regions of the molecules. The N-terminal regions of histone molecules interact with the DNA molecule in such a way that the latter is wound onto the histone backbone, making two turns on one side and one on the other. There are about 140 DNA base pairs per nucleosome. Between adjacent nucleosomes there is a DNA segment varying in length (10-70 base pairs). When it is straightened, the DNA takes the form of a strand of beads. If the segment is folded, the nucleosomes are closely adjacent to each other, forming a fibril 10 nm in diameter. The structure of nucleosomal particles is the principle of the organization of chromatin (see) both in the interphase and in the metaphase chromosome.

Individually distinguishable chromosomes are formed by time cell division, mitosis or meiosis, as a result of progressively increasing condensation of chromosomes. In the prophase of mitotic division, chromosomes are visible under a light microscope in the form of long and intertwined threads, therefore, individual chromosomes are indistinguishable throughout. In the prophase of the first meiotic division, chromosomes undergo complex specific morphological transformations, associated mainly with the conjugation of homologous chromosomes (see Chromosome conjugation) and genetic recombination (exchange of sites) between them. In pachytene (when conjugation ends), the alternation of chromomeres along the length of chromosomes is especially indicative, and the chromomeric pattern is specific for each chromosome and changes with condensation. Many chromosomes in oogenesis and the Y chromosome in spermatogenesis have high transcriptional activity. In some types of organisms, such chromosomes are called "lamp brushes". They consist of an axis built of chromomeres and interchromomeric regions, and numerous side loops - decondensed chromomers in a state of genetic functioning (transcription).

In the metaphase of cell division, chromosomes have the smallest length and are easy to investigate, therefore, a description of individual chromosomes, as well as of their entire set in a cell, is given in relation to their state in this phase. The sizes of metaphase chromosomes in one and the same type of organisms differ greatly: chromosomes of a fraction of a micron have a dotted appearance, with a length of more than 1 micron they look like rod-shaped bodies. Usually these are formations bifurcated along the length, consisting of two sister chromatids (Fig. 2, 3), since chromosomes are reduplicated in metaphase.

Individual chromosomes of a set differ in length and other morphological characteristics. The methods used until the 70s ensured uniform staining of the chromosome along its length. Nevertheless, such a chromosome, as an obligatory structural element, has a primary constriction - a region where both chromatids are narrowed, apparently not separating from one another, and are poorly stained. This region of the chromosome is called the centromere, it contains a specialized structure - the kinetochore, which is involved in the formation of spindle filaments of chromosome division. According to the ratio of the sizes of the chromosome arms lying on both sides of the primary constriction, chromosomes are divided into three types: metacentric (with a medial constriction), submetacentric (the constriction is displaced from the middle), acrocentric (the centromere is located close to the end of the chromosome, Fig. 3). A person has all three types of chromosomes. The ends of the chromosomes are called telomeres. Along the length of the chromosomes, with varying degrees of constancy, there can be found not related to the centromere, the so-called secondary constrictions. If they are located close to the telomere, the distal portion of the chromosome separated by the constriction is called the satellite, and the constriction is called the satellite (Fig. 2). A person has ten chromosomes with a secondary constriction, all of them are acrocentric, satellites are localized in the short shoulder. Some secondary constrictions contain ribosomal genes and are called nucleolar-forming, because due to their functioning in the production of RNA in the interphase nucleus, a nucleolus is formed (see). Other secondary constrictions are formed by heterochromatic regions of chromosomes; in humans, of such constrictions, the most pronounced pericentromeric constrictions are in the 1st, 9th and 16th chromosomes.

The original method of using Giemsa and other chromosomal dyes produced uniform coloration along the entire length of the chromosome. Since the beginning of the 70s, a number of methods for staining and processing metaphase chromosomes have been developed, which made it possible to detect differentiation (division into light and dark stripes) of the linear structure of each chromosome along its entire length: with the help of akrikhin, acrihiniprita and other fluorochromes; G-staining (G - from the name Giemsa), obtained with the help of Giemsa dye (see Romanovsky - Giemsa method) after incubation of chromosome preparations under special conditions; R-color (R - from the English reverse reverse; chromosomes are colored back by G-color). The body of the chromosome is subdivided into segments of different intensity of staining or fluorescence. The number, position and size of such segments are specific for each chromosome, so any chromosome set can be identified. Other methods allow for differential staining of separate specific regions of chromosomes. Selective staining with Giemsa dye of heterochromatic regions of the chromosome (C-color; C - from centromere centromere), located near the centromere - C-segments (Fig. 4). In humans, C-segments are found in the pericentromeric region of all autosomes and in the long arm of the Y-chromosome. Heterochromatic regions vary in size in different individuals, causing chromosome polymorphism (see Chromosomal polymorphism). Specific colors make it possible to identify nucleolar-forming regions functioning in the interphase, as well as kinetochores, in metaphase chromosomes.

At the electron microscopic level, the main ultrastructure unit of interphase chromatin in transmission electron microscopy (see) is a thread with a diameter of 20-30 nm. The packing density of filaments is different in areas of dense and diffuse chromatin.

A metaphase chromosome on a section in a transmission electron microscope appears to be uniformly filled with fibrils 20-30 nm in diameter, which, depending on the section plane, have the form of round, oval or elongated formations. In prophase and telophase, thicker filaments (up to 300 nm) can be found in the chromosome. In electron microscopy, the surface of the metaphase chromosome is represented by randomly stacked numerous fibrils of different diameters, visible, as a rule, on a short segment (Fig. 5). Filaments with a diameter of 30-60 nm predominate.

Variability of chromosomes in ontogeny and evolution

The constancy of the number of chromosomes in the chromosome set and the structure of each chromosome is an indispensable condition for normal development in ontogenesis (see) and preservation of biol. species. During the life of an organism, changes in the number of individual chromosomes and even their haploid sets (genomic mutations) or the structure of chromosomes (chromosomal mutations) can occur. Unusual variants of chromosomes, which determine the uniqueness of an individual's chromosome set, 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 taxonomy of species (karyosystematics). In animals, one of the main mechanisms of evolutionary 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 the chromosomes of humans and modern apes made it possible, on the basis of the similarities and differences in individual chromosomes, to establish the degree of phylogenetic relationship of these species and to model the karyotype of their common closest ancestor.

Bochkov N. P., Zakharov A. F. and Ivanov V. I. Medical genetics, M., 1984; Darlington S. D. and La Cours L. F. Chromosomes, Methods of work, trans. from English, M., 1980, bibliogr .; Zakharov A.F. Human chromosomes (problems of linear organization ;, M., 1977, bibliogr .; Zakharov A.F. et al. Human chromosomes, Atlas, M., 1982; Kiknadze I.I. Functional organization of chromosomes, L. , 1972, bibliogr .; Fundamentals of human cytogenetics, under the editorship of A.A. ; 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; Therman E. Human chromosomes, NY ao, 1980.

A.F. Zakharov.

Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made from a protein and a single DNA molecule, which contains the body's genetic instructions, passed on from the parents. In humans, animals, and plants, most chromosomes are located in pairs within the cell nucleus. Humans have 22 of these chromosome pairs, called autosomes.

Humans have 22 pairs of chromosomes and two sex chromosomes. Women have two X chromosomes; males have an X chromosome and a Y chromosome.

How gender is determined

Humans have an extra pair of sex chromosomes for a total of 46 chromosomes. The sex chromosomes are called X and Y, and their combination determines a person's gender. Typically, women have two X chromosomes, while men have XY chromosomes. This XY sexing system is found in most mammals as well as some reptiles and plants.

The presence of XX or XY chromosomes is determined when the sperm fertilizes the egg. Unlike other cells in the body, cells in the egg and sperm, called gametes or sex cells, have only one chromosome. Gametes are produced by cell division in meiosis, which results in the separated cells having half the number of chromosomes as parent or progenitors. In the case of humans, this means that the parent cells have two chromosomes and they have one gamete.

All gametes in mothers' eggs have X chromosomes. The father's sperm contains about half of the X and half of the Y chromosomes. Sperm is a variable factor in determining the sex of a child. If the sperm carries the X chromosome, it will combine with the X chromosome of the egg to form a female zygote. If the semen carries the Y chromosome, it will lead to the birth of a boy.

During fertilization, the gametes from the sperm combine with the gametes from the egg to form a zygote. The zygote contains two sets of 23 chromosomes for the required 46. Most females are 46XX and most males are 46XY, according to the World Health Organization.

However, there are some options. Recent research has shown that a person can have many different combinations of sex chromosomes and genes, especially those who identify as LGBT. For example, a specific X chromosome called Xq28 and a gene on chromosome 8 appears to be found at a higher prevalence in gay men, according to a 2014 study in the journal Psychological Medicine.

Several out of a thousand babies are born with one sex chromosome (45X or 45Y), this is called monosomy. Others are born with three or more sex chromosomes (47XXX, 47XYY or 47XXY, etc.), this is called polysomy. “In addition, some males are born with 46XX due to the translocation of a tiny portion of the sex that defines the Y chromosome region,” reports the WHO. “Likewise, some women are also born 46XY due to mutations in the Y chromosome. Obviously, not only are women who are XX and men XY, but rather there are a number of chromosome additions, hormonal balances and phenotypic variations. "

X and Y chromosome structure

While the chromosomes for other parts of the body are the same size and shape, forming an identical pairing - the X and Y chromosomes have different structures.

The X chromosome is significantly longer than the Y chromosome and contains hundreds of more genes. Since the additional genes on the X chromosome have no counterparts on the Y chromosome, the X genes are dominant. This means that almost any gene on X, even if it is recessive in the female, will be expressed in the males. These are called X-linked genes. Genes found only on the Y chromosome are called Y-linked genes and are only expressed in males. Genes on any sex chromosome can be called sex genes.

There are approximately 1,098 X-linked genes, although most are not for female anatomical characteristics. In fact, many of them are associated with disorders such as hemophilia, Duchenne muscular dystrophy, and several others. They are most commonly found in men. Non-sex characteristics of X-linked genes are also responsible for male pattern baldness.

Unlike the large X chromosome, the Y chromosome contains only 26 genes. Sixteen of these genes are responsible for maintaining cells. Nine are involved in sperm production, and if some are missing or defective, low sperm counts or infertility can occur. One gene, called the SRY gene, is responsible for male sex traits. The SRY gene triggers the activation and regulation of another gene found on the non-sex chromosome called Sox9. Sox9 triggers the development of the non-sex gonads into the testes instead of the ovaries.

Sex chromosome abnormalities

Abnormalities in the combination of sex chromosomes can lead to a variety of gender-specific conditions that are rarely fatal.

Female abnormalities lead to Turner Syndrome or Trisomy X. Turner Syndrome occurs when women have only one X chromosome instead of two. Symptoms include genital failure from normal maturity, which can lead to infertility, small breasts, and no menstruation; short stature; wide, thyroid chest; and a wide neck.

Trisomy X syndrome is caused by three X chromosomes instead of two. Symptoms include tall stature, speech delays, premature ovarian failure or ovarian abnormalities, and weak muscle tone - although many girls and women show no symptoms.

Klinefelter's syndrome can affect men. Symptoms include breast development, abnormal proportions such as large hips, tall stature, infertility, and small testicles.

Chromosome is the organized structure of DNA and protein contained in cells. It is one piece of coiled DNA containing many genes, regulatory elements, and other nucleotide sequences. Chromosomes also contain proteins associated with DNA that are used to package DNA and control its functions. Chromosomal DNA encodes all or most of the genetic information in an organism; some species also contain plasmids or other extrachromosomal genetic elements.

Or Down's disease, also known as trisomy 21, is an inherited disorder caused by the presence of part or all of 3 copies of 21 chromosomes... Usually, it is associated with retardation of physical development, characteristic features of the face, or mild to moderate intellectual ...

Chromosomes vary widely between different organisms. A DNA molecule can be round or linear, and can have anywhere from 100,000 to over 3,750,000,000 nucleotides in a long chain. Typically, eukaryotic cells (cells with nuclei) have large linear chromosomes, and prokaryotic cells (cells without specific nuclei) have smaller round chromosomes, although there are many exceptions to this rule. In addition, the cells may contain chromosomes of several types; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own little chromosomes.

In eukaryotes, nuclear chromosomes are packed by proteins into a condensed structure called chromatin. This allows very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies throughout the cell cycle. Chromosomes are an essential building block for cell division and must reproduce, divide and pass successfully to their daughter cells in order to ensure genetic diversity and the survival of their offspring. Chromosomes can be duplicated or non-duplicated. Non-duplicated chromosomes are single linear strands in which duplicated chromosomes contain two identical copies (called chromatids) united by a centromere.

Densification of duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure. Chromosomal recombination plays a vital role in genetic diversity. If these structures are improperly manipulated through processes known as chromosomal instability and translocation, the cell can undergo mitotic catastrophe and die, or it can unexpectedly escape apoptosis, leading to cancer progression.

In practice, "chromosome" is a rather vague term. For prokaryotes and viruses lacking chromatin, the term genophore is more appropriate. In prokaryotes, DNA is usually organized in a loop that coils tightly around itself, sometimes accompanied by one or less round DNA molecules called plasmids. These small, round genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origin. The simplest genophores are found in viruses: these are DNA or RNA molecules - short linear or round genophores that are often devoid of structural proteins.

Word " chromosome"Formed by the Greek words" χρῶμα "( chroma, color) and "σῶμα" ( soma, body) due to the property of chromosomes to undergo very strong staining with certain dyes.

History of the study of chromosomes

In a series of experiments begun in the mid-1880s, Theodore Boveri has definitely demonstrated that chromosomes are vectors of heredity. His two principles were sequence chromosomes and individuality chromosomes. The second principle was very original. Wilhelm Roux suggested that each chromosome carries a different genetic load. Boveri was able to test and confirm this hypothesis. By rediscovering from an early work by Gregor Mendel in the early 1900s, Boveri was able to mark the connection between the rules of inheritance and the behavior of chromosomes. Boveri influenced two generations of American cytologists: among them Edmund Beecher Wilson, Walter Sutton, and Theophilus Painter (in fact, Wilson and Painter worked with him).

In his famous book “ Cell in development and heredity Wilson tied together the independent work of Boveri and Sutton (circa 1902), calling the chromosomal theory of heredity the Sutton-Boveri theory (names are sometimes interchanged). Ernst Mayr notes that the theory has been hotly contested by some famous geneticists such as William Bateson, Wilhelm Johansen, Richard Goldschmidt, and T.H. Morgan, they all had a rather dogmatic mindset. In the end, complete proof was obtained from chromosome maps in Morgan's own laboratory.

Prokaryotes and chromosomes

Prokaryotes - bacteria and archaea - usually have one round chromosome, but there are many variations.

In most cases, the size of the chromosomes of bacteria can range from 160,000 base pairs in an endosymbiotic bacterium Candidatus Carsonella ruddii up to 12,200,000 bp in soil-dwelling bacteria Sorangium cellulosum... Spirochetes of the genus Borrelia are a remarkable exception to this classification, along with bacteria such as Borrelia burgdorferi(the cause of Lyme disease) containing one linear chromosome.

Structure in sequences

Chromosomes in prokaryotes have a smaller structure based on sequence than eukaryotes. Bacteria usually have one point (duplication origin) where duplication begins, while some archaea contain multiple points of duplication origin. Genes in prokaryotes are often organized into operons and usually do not contain introns, unlike eukaryotes.

DNA packaging

Prokaryotes do not have nuclei. Instead, their DNA is organized into a structure called a nucleoid. A nucleoid is a separate structure that occupies a specific area of a bacterial cell. However, this structure is dynamic, maintained and transformed by the actions of histone-like proteins that bind to the bacterial chromosome. In archaea, the DNA in the chromosomes is even more organized, with the DNA packed into structures similar to those of eukaryotes.

Bacterial chromosomes tend to bind to the bacterial plasma membrane. In molecular biological applications, this allows its isolation from plasmid DNA by centrifuging the lysed bacterium and precipitating the membranes (and attached DNA).

Chromosomes of prokaryotes and plasmids are, like eukaryotic DNA, generally supercoiled. DNA must first be isolated in a weakened state in order to access transcription, regulation, and duplication.

In eukaryotes

Eukaryotes (cells with nuclei found in plants, yeast, and animals) have large linear chromosomes found in the cell nucleus. Each chromosome has one centromere, with one or two arms protruding from the centromere, although in most circumstances these arms are not visible as such. In addition, most eukaryotes have one round mitochondrial genome, and some eukaryotes may have additional small round or linear cytoplasmic chromosomes.

In the nuclear chromosomes of eukaryotes, unconsolidated DNA exists in a semi-ordered structure where it is wrapped around histones (structural proteins) to form a composite material called chromatin.

Chromatin

Chromatin is a complex of DNA and protein found in the nucleus of the eukaryote that packages chromosomes. The structure of chromatin varies significantly between different stages of the cell cycle, in accordance with the requirements of the DNA.

Interphase chromatin

During the interphase (the period of the cell cycle when the cell is not dividing), two types of chromatin can be distinguished:

Euchromatin, which is composed of active DNA, that is, expressed as a protein.
Heterochromatin, which is composed mostly of inactive DNA. It appears to serve structural purposes during chromosomal stages. Heterochromatin can be further classified into two types:

Constitutive heterochromatin never expressed. It is located around the centromere and usually contains repeated sequences.
Optional heterochromatin, sometimes expressed.

Metaphase chromatin and division

In the early stages of mitosis or meiosis (cell division), the chromatin strands become increasingly dense. They cease to function as available genetic material (transcription stops) and become a compact transportable form. This compact shape makes the individual chromosomes visible, and they form the classic four-arm structure, with a pair of sister chromatids attached to each other at the centromere. Shorter arms are called " p shoulders"(From the French word" petit "- small), and longer shoulders are called " q shoulders"(Letter" q"Follows the letter" p»In the Latin alphabet; q-g "grande" is large). This is the only natural context in which individual chromosomes are visible with an optical microscope.

During mitosis, microtubules grow from centrosomes located at opposite ends of the cell and also attach to the centromere in specialized structures called kinetochores, one of which is present on each sister chromatid. A special sequence of DNA bases in the kinetochore region, together with special proteins, ensures long-term attachment to this region. Microtubules then pull chromatids to centrosomes so that each daughter cell inherits one set of chromatids. When the cells are divided, the chromatids unwind and the DNA can be transcribed again. Despite their appearance, chromosomes are structurally highly condensed, which allows these giant DNA structures to fit into the cell nucleus.

Human chromosomes

Chromosomes in humans can be classified into two types: autosomes and sex chromosomes. Certain genetic traits are associated with a person's sex and are passed on through the sex chromosomes. Autosomes contain the rest of the inherited genetic information. Everyone acts the same way during cell division. Human cells contain 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes), giving a total of 46 per cell. In addition, human cells contain many hundreds of copies of the mitochondrial genome. Sequencing the human genome provided a lot of information about each chromosome. Below is a table that compiles statistics for chromosomes based on the Sanger Institute's human genome information in the VEGA (Vertebrate Genome Commentary) database. The number of genes is a rough estimate as it is based in part on gene prediction. The total length of the chromosomes is also a rough estimate based on the estimated size of the regions of inconsistent heterochromatins.

Chromosomes	Genes	Total number of complementary base pairs nucleic acids	Ordered complementary nucleic acid base pairs






















X ( sex chromosome)
Y (sex chromosome)
Total		3079843747	2857698560

The number of chromosomes in various organisms

Eukaryotes

These tables give the total number of chromosomes (including sex) in the cell nuclei. For example, diploid human cells contain 22 different types of autosomes, each with two copies, and two sex chromosomes. This gives 46 chromosomes in total. Other organisms have more than two copies of their chromosomes, for example, hexaploid bread wheat contains six copies of seven different chromosomes, for a total of 42 chromosomes.

The number of chromosomes in some plants
Plant species
Arabidopsis thaliana(diploid)

Garden snail
Tibetan fox
Domestic pig
Laboratory rat
Syrian hamster

Domestic sheep


Kingfisher
Silkworm

The number of chromosomes in other organisms
Kinds	Large chromosomes	Intermediate chromosomes	Microchromosomes
Trypanosoma brucei
Domestic pigeon ( Columba livia domestics)
		2 sex chromosomes

Normal members of certain eukaryotic species have the same number of nuclear chromosomes (see table). Other chromosomes of eukaryotes, that is, mitochondrial and plasmid-like small chromosomes, vary considerably in number, and there can be a thousand copies per cell.

Asexually reproducing species have one set of chromosomes, the same ones found in the cells of the body. However, asexual species can be haploid and diploid.

Sexually reproducing species have somatic cells (body cells) that are diploid, having two sets of chromosomes, one from the mother and the other from the father. Gametes, reproductive cells, are haploid [n]: they have one set of chromosomes. Gametes are obtained by meiosis of a diploid germ line cell. During meiosis, the corresponding chromosomes of the father and mother can exchange small parts of each other (crossing), and thus form new chromosomes that are not inherited only from one or the other parent. When the male and female gametes combine (fertilization), a new diploid organism is formed.

Some species of animals and plants are polyploid: they have more than two sets of homologous chromosomes. Agriculturally important plants such as tobacco or wheat are often polyploid compared to hereditary species... Wheat has a haploid number of seven chromosomes found in some cultivated plants as well as in wild ancestors. The more common pasta and bread wheat are polyploid, having 28 (tetraploid) and 42 (hexaploid) chromosomes, compared to 14 (diploid) chromosomes in wild wheat.

Prokaryotes

Prokaryotic species generally have one copy of each major chromosome, but most cells can easily survive with multiple copies. For instance, Buchnera, a symbiont of aphids, has many copies of its chromosome, the number of which ranges from 10 to 400 copies per cell. However, in some large bacteria such as Epulopiscium fishelsoni, up to 100,000 copies of a chromosome may be present. The copy number of plasmids and plasmid-like small chromosomes, as in eukaryotes, fluctuates considerably. The number of plasmids in a cell is almost entirely determined by the rate of plasmid division — rapid division produces a high copy number.

Karyotype

Generally karyotype is a characteristic chromosomal complement of eukaryotic species. Preparing and studying karyotypes is part of cytogenetics.

Although DNA duplication and transcription is highly standardized in eukaryotes, the same cannot be said for their karyotypes which are usually quite volatile. The types of chromosome numbers and their detailed organization can vary. In some cases, there can be significant variation between species. Often there is:

oscillation between the two sexes;
oscillation between the germ line and the soma (between the gametes and the rest of the body);
fluctuation between members of the population due to balanced genetic polymorphism;
geographic variation between races;
mosaic or other anomalies

Also, fluctuations in the karyotype can occur during development from a fertilized egg.

The technique for determining the karyotype is usually called karyotyping... Cells can be blocked partially through division (in metaphase) in vitro (in a reaction tube) with colchicine. These cells are then stained, photographed, and arranged in a karyogram, with a set of ordered chromosomes, autosomes in length order, and sex chromosomes (here X / Y) at the end.

As with many sexually reproducing species, humans have special gonosomes (sex chromosomes, as opposed to autosomes). It is XX for women and XY for men.

Historical note

It took many years to study the human karyotype before the most basic question was answered: How many chromosomes are there in a normal diploid human cell? In 1912, Hans von Winewarter reported 47 chromosomes in spermatogonia and 48 in oogonia, including the XX / XO sex determination mechanism. Painter in 1922 was not sure about the diploid number of a person - 46 or 48, at first leaning towards 46. He later revised his opinion from 46 to 48, and correctly insisted that a person possesses the XX / XY system.

To finally solve the problem, new techniques were needed:

The use of cells in culture;
Preparing cells in a hypotonic solution, where they swell and spread chromosomes;
Delay of mitosis in metaphase with colchicine solution;
Crushing the preparation on the object holder, stimulating the chromosomes in a single plane;
Cutting the photomicrograph and sequencing the results into an irrefutable karyogram.

Only in 1954 was the diploid number of a person confirmed - 46. Given the techniques of Winiwarter and Painter, their results were quite remarkable. Chimpanzees (the closest living relative of modern humans) have 48 chromosomes.

Delusions

Chromosomal abnormalities are abnormalities in the normal chromosomal content of a cell and are a major cause of genetic conditions in humans, such as Down syndrome, although most abnormalities have little or no effect. Some chromosomal abnormalities do not cause disease in carriers, such as translocations or chromosomal inversions, although they can lead to an increased chance of having a baby with a chromosomal abnormality. An abnormal number of chromosomes, or chromosome sets called aneuploidy, can be fatal or give rise to genetic disorders. Families who may carry a chromosomal rearrangement are offered genetic counseling.

The recruitment or loss of DNA from chromosomes can lead to a variety of genetic disorders. Examples among humans:

Feline scream syndrome, caused by the division of a portion of the short arm of chromosome 5. The condition is so named because children who are sick make shrill, cat-like screams. People with this syndrome have wide-set eyes, small heads and jaws, moderate to severe mental health problems, and short stature.
Down syndrome, the most common trisomy, is usually caused by an extra copy of chromosome 21 (trisomy 21). Signs include decreased muscle tone, stocky build, asymmetrical cheekbones, slanted eyes, and mild to moderate developmental disabilities.
Edwards syndrome, or trisomy of chromosome 18, is the second most common trisomy. Symptoms include slow movement, developmental disorders, and multiple congenital anomalies that cause serious health problems. 90% of patients die in infancy. They are characterized by clenched fists and overlapping fingers.
Isodicentric chromosome 15, also called idic (15), partial tetrasomy of the long arm of chromosome 15, or reverse duplication of chromosome 15 (inv dup 15).
Jacobsen's syndrome is very rare. It is also called a disorder of the terminal deletion of the long arm of chromosome 11. Sufferers have normal intelligence or weak developmental disabilities, with poor speech skills. Most have a bleeding disorder called Paris-Trousseau syndrome.
Klinefelter's syndrome (XXY). Men with Klinefelter syndrome are usually sterile, usually taller, and have longer arms and legs than their peers. Boys with the syndrome are usually shy and quiet, and are more likely to have speech delay and dyslexia. Without testosterone treatment, some may develop gynecomastia during adolescence.
Patau syndrome, also called D-syndrome or trisomy 13 of chromosome. Symptoms are somewhat similar to trisomy 18, without the characteristic folded arm.
Small accessory marker chromosome. This means there is an extra abnormal chromosome. Properties depend on the origin of the additional genetic material. Cat eye syndrome and isodicentric 15 (or idic15) syndrome are caused by an extra marker chromosome, like Pallister-Killian syndrome.
Triple X syndrome (XXX). XXX girls tend to be taller, thinner and more likely to be dyslexic.
Turner syndrome (X instead of XX or XY). In Turner syndrome, female sexual characteristics are present, but underdeveloped. Women with Turner syndrome have a short torso, a low forehead, anomalies in the eyes and bones, and a concave chest.
XYY syndrome. XYY boys are usually taller than their siblings. Like XXY boys and XXX girls, they are more likely to have learning difficulties.
Wolf Hirschhorn syndrome, which is caused by partial destruction of the short arm of chromosome 4. It is characterized by severe growth retardation and severe mental health problems.