Normal human somatic cells contain 46 chromosomes, forming 23 homologous pairs; The 22 pairs of chromosomes that are identical in males and females are called autosomal ( autosomes); The 23rd pair of chromosomes, which differs between men and women, is a pair sex chromosomes.
In women, the sex chromosomes are represented by two identical (homologous) chromosomes (XX), in men - chromosomes that differ in size and shape (X and Y).
All chromosomes of human cells are paired, i.e. each chromosome has its homologue genes similar in size, shape and features, and make up a double (2n), or diploid, kit; single (1n), or haploid, only mature germ cells have a set of chromosomes.
In addition to the number of chromosomes (chromosome set), the human karyotype is characterized by morphological features of chromosomes .
Structurally, the metaphase chromosome consists of twochromatids, each of which has twoshoulder And centromere, or the primary constriction, which acts as the mechanical center of the chromosome during division. The centromere is the region of the chromosome to which the filament is attached during cell division.fission spindle in area kinetochore,distributing chromosomes to the poles of the cell. In addition to the primary constriction, some chromosomes havesecondary constriction, not related to the process of attaching the spindle threads. The location of the secondary constriction in the chromosome is associated with the formation of the nucleolus, and this region of the chromosome is callednucleolar organizer.The long arm of the chromosome is denoted by the Latin letter "q", the short - "p".
The end sections of the chromosomes have segments that prevent the ends of the chromosomes from sticking together, and thereby contribute to the preservation of their integrity. These segments have been named telomeres.
There are several types of chromosomes depending on the location of the centromere:
metacentric chromosomes(equal-arm) - the centromere is located in the center of the chromosome and, as it were, divides it into equal parts;
submetacentric chromosomes- one shoulder is slightly larger than the other;
acropentric chromosomes have an almost terminal (terminal) position of the centromere, i.e. one shoulder is much larger than the other; some acrocentric chromosomes have so-called satellites - regions connected to the rest of the chromosome by a thin filament of chromatin ( satellite chromosomes); the size of the satellite relative to the length of the entire chromosome is constant for each specific chromosome (in the human karyotype, five pairs of chromosomes have satellites: 13th, 14th, 15th, 21st and 22nd).
Depending on the morphology and size, pairs of human chromosomes are divided into 7 groups, denoted by Latin letters from A to G (pairs of chromosomes from morphologically larger towards smaller sizes are numbered with Arabic numerals).
Group A (1-3rd) - the largest chromosomes; 1st and 3rd - metacentric, 2nd - submetacentric.
Group B (4th and 5th) - large submetacentric chromosomes.
Group C (chromosome 6-12 and X) - submetacentric chromosomes of medium size.
Group D (13-15th) - acrocentric chromosomes of medium size.
Group E (16-18th) - small submetacentric chromosomes.
Group F (19th and 20th) - the smallest metacentric chromosomes.
Group G (21st, 22nd and Y) are the smallest acrocentric chromosomes.
All human diseases, taking into account the role hereditary factors can be divided into three groups:
1. Hereditary diseases that develop only in the presence of a mutant gene; they are passed from generation to generation through germ cells; for example, some forms of muscular dystrophy, myopia, six-fingeredness.
2. Diseases with hereditary predisposition; in this case, it is not the diseases themselves that are transmitted, but the predisposition to them; additional external harmful influences are necessary for the development of such diseases; eg epilepsy, certain allergic conditions, hypertension.
3. Diseases caused by various infectious agents are caused by trauma and do not directly depend on heredity. However, in these cases it also plays a role. It is known that in some families there are several patients with tuberculosis, in others - children often suffer from colds. Not all people who have contact with infectious patients fall ill, and, finally, it cannot be ruled out that hereditary characteristics of the organism play a certain role in the diversity of the course of the disease.
Chromosomal diseases or chromosomal syndromes are complexes of multiple congenital malformations caused by numerical or structural changes in chromosomes that are visible under a light microscope.
Violations in the structure of chromosomes, changes in their number, gene mutations can occur at different stages of the development of the organism. If they arise in the gametes of the parents, then the anomaly will be observed in all cells of the body (full mutant).
If they arise during embryonic development, the chromosome set in different cells of the body will be different. In the process of development, several successive generations of cells with different chromosome sets appear. With a small number of abnormal cells, the disease may not occur in the future.
1. The concept of autosomes, their number, functions.
Chromosomes consist of 2 sister chromatids (doubled DNA molecules) connected to each other in the region of the primary constriction - the centromere. The centromere divides the chromosome into 2 arms. Depending on the location of the centromere, the chromosomes are; 1) the metacentric centromere is located in the middle of the chromosome and its arms are equal; 2) submetacentric centromere is displaced from the middle of the chromosomes and one arm is shorter than the other; 3) acrocentric - the centromere is located close to the end of the chromosome. And one shoulder is much shorter than the other. Some chromosomes have secondary constrictions that separate from the chromosome arm a region called the satellite, from which the nucleolus is formed in the interphase nucleus,
Chromosome Rules
1. The constancy of the number of chromosomes.
Somatic cells of an organism of each species have a strictly defined number of chromosomes (in humans -46)
2. Pairing of chromosomes.
Each. the chromosome in somatic cells with a diploid set has the same homologous (same) chromosome, identical in size, shape, but unequal in origin: one from the father, the other from the mother.
3. The rule of individuality of chromosomes.
Each pair of chromosomes differs from the other pair in size, shape, alternation of light and dark stripes.
4. The rule of continuity.
Before cell division, the DNA is doubled and the result is 2 sister chromatids. After division, one chromatid enters the daughter cells, so the chromosomes are continuous: a chromosome is formed from a chromosome.
All chromosomes are divided into autosomes and sex chromosomes. Sexual - this is the 23rd pair of chromosomes, which determines the formation of the male 11th female body.
Autosomes - all chromosomes in cells, with the exception of sex chromosomes, there are 22 pairs.
In somatic cells, it is present. double - a diploid set of chromosomes, in sex -, haploid (single). The chromosome set of a healthy person is 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (female - XX, male - XY).
A certain set of chromosomes of a cell, characterized by the constancy of their number, size and shape, is called a karyotype.
In order to understand a complex set of chromosomes, they are arranged in pairs as their size decreases, taking into account! the position of the centromere and the presence of secondary constrictions. Such a systematized karyotype is called an idiogram.
To study the karyotype of genetics, the method of cytogenetic analysis is used, in which a number of hereditary diseases associated with a violation of the number and shape of chromosomes.
Etiological factors of chromosomal pathology are all types of chromosomal mutations (chromosomal aberrations) and some genomic mutations (changes in the number of chromosomes). There are only 3 types of genomic mutations found in humans: tetraploidy, triploidy, and aneuploidy. Of all the variants of aneuploidy, only trisomy for autosomes, polysomy for sex chromosomes (tri-, tetra- and pentasomy) are found, and from monosomy - only monosomy X.
All types of chromosomal mutations have been found in humans: deletions, duplications, inversions and translocations. A deletion (lack of a site) in one of the homologous chromosomes means a partial monosomy for this site, and a duplication (doubling of a site) means a partial trisomy.
Inheriting such altered chromosomes from one of the parents will be partial monosomy in one or two terminal sections of the chromosome. Translocations - the transfer of a site from one chromosome to another or to another place on the same chromosome.
Outcomes - death, congenital malformations, high risk of birth of sick children. For example, the fusion of 2 chromosomes into one (Down syndrome) - 21 chromosomes with the 14th or 15th.
Inversion - when a chromosome breaks in two places, the freed area unfolds by 180% and again rises to its original place.
Outcomes - spontaneous abortions, multiple congenital malformations, minor developmental anomalies, mental retardation, no anomalies.
deletion - the disappearance of the torn off part of the chromosomes. Each chromosome has a long and a short arm. The short arm is denoted by the small Latin letter "r", the long arm - "q". The lack of any one arm of the chromosome is indicated by the corresponding Latin letter, after which the “-” sign is put, and the number in front of the letter indicates the serial number of the abnormal chromosome.
The study of a human karyotype under a microscope is carried out using the cytogenetic method.
Karyotype-a set of chromosomes characteristic of the somatic cells of a given organism.
Ideogram (systematized karyotype) - graphic image chromosomes, taking into account their absolute and relative length, centromeric index, the presence of a second constriction and a satellite.
The concept of Karyotype was introduced by Sov. geneticist G. A. Levitsky (1924). Karyotype is one of the most important genetic characteristics of a species, since each species has its own karyotype, which differs from the karyotype of related species (this is the basis of a new branch of taxonomy - the so-called karyosystematics). The constancy of the karyotype in the cells of one organism is ensured by mitosis, and within the species - by meiosis. The karyotype of an organism can change if germ cells (gametes) undergo changes under the influence of mutations. Sometimes the karyotype of individual cells differs from the species karyotype as a result of chromosomal or genomic so-called somatic mutations. The karyotype of diploid cells consists of 2 haploid sets of chromosomes (genomes) obtained from one or another parent; each chromosome of such a set has a homologue from another set. The karyotype of males and females may differ in the shape (sometimes also in the number) of the sex chromosomes, in which case they are described separately. Chromosomes in the karyotype are examined at the metaphase stage of mitosis. Description The karyotype must be accompanied by a photomicrograph or a sketch. For systematization, the karyotype of a pair of homologous chromosomes is arranged, for example, in decreasing length, starting with a long pair; pairs of sex chromosomes are placed at the end of the row.
Pairs of chromosomes that do not differ in length are identified by the position of the centromere (primary constriction), which divides the chromosome into 2 arms, the nucleolar organizer (secondary constriction), the shape of the satellite, and other features. The karyotypes of several thousand wild and cultivated species of plants, animals, and humans have been studied.
Autosomes - paired chromosomes, the same for male and female organisms. There are 44 autosomes in the cells of the human body (22 pairs)
Sex chromosomes - chromosomes containing genes that determine the sex characteristics of an organism.
In the karyotype (qualitative and quantitative set of chromosomes) of women, the sex chromosomes are the same. In the karyotype of a man - 1 one large equal-armed sex chromosome, the other is a small rod-shaped chromosome.
The female sex chromosomes are designated XX and the male sex chromosomes are XY. The female body forms gametes with the same sex chromosomes (homogametic organism), and the male body forms gametes that are not the same for the sex chromosomes (X and Y).
In birds, butterflies, and some species of fish, the male sex is homogametic. In a rooster, the karyotype is designated XX, and in a chicken, XY.
24. Gender, its predestination (progamous, syngamous, epigamous).
Floor - it is a set of signs and properties of an organism that determine its participation in reproduction.
The sex of an individual can be determined:
a) before the fertilization of the egg by the spermatozoon (software sex determination);
b) at the time of fertilization (syngamous sex determination);
c) after fertilization (epigamous sex determination).
Before fertilization, sex is determined in some organisms as a result of the division of eggs into fast-growing and slow-growing ones. The first (larger) after merging with the male gamete give females, and the second (small) - males. In rotifers, capable of reproducing in addition to the usual sexual reproduction with fertilization, parthenogenetically, part of the parthenogenetic eggs lose half of the chromosomes during development. Males develop from such eggs, and the rest gives rise to females.
In the marine annelid worm Bonellia, sex determination occurs in the process of ontogenesis: if the larva sits on the bottom, a female develops from it, and if it attaches to the proboscis of an adult female, then a male.
In the vast majority of eukaryotes, the sex is laid at the time of fertilization and is determined genotypically by the chromosome set that the zygote receives from the parents. The cells of male and female animals differ in a pair of chromosomes. This pair is called sex chromosomes (heterosomes), as opposed to the rest - autosomes. The sex chromosomes are commonly referred to as the X and Y chromosomes. Depending on their combination in and organisms, 5 types of chromosomal sex determination are distinguished:
1) XX, XO (O means no chromosomes) occurs in Protenor species (insects);
2) XX, XY - it is typical, for example, for Drosophila, mammals (including humans);
3) XY, XX - this type of sex determination is typical for butterflies, birds, reptiles;
4) XO, XX - observed in aphids;
5) the haplodiploid type (2n, n) is found, for example, in bees: males develop from unfertilized haploid eggs, females from fertilized diploid ones.
The specific mechanisms linking the development of male or female with a certain combination of sex chromosomes in different organisms is different. In humans, for example, sex is determined by the presence of the Y chromosome: it contains the TDP gene, it encodes the testicle, a determining factor that determines the development of the male sex.
In Drosophila, on the Y chromosome, there is a fertility gene responsible for male fertility, and sex is determined by the balance of the number of X chromosomes and the number of sets of autosomes (an ordinary diploid organism contains, respectively, two sets of autosomes). The genes that determine development along the path of the female are located on the X chromosomes, and on the autosomes - along the path of the male.
If the ratio of the number of X chromosomes to the number of sets of autosomes is 0.5, then a male develops, and if it is 1, then a female develops.
In addition to normal males and females, intersexes sometimes appear - individuals that, according to their sexual characteristics, occupy an intermediate position between the male and female sexes (not to be confused with hermaphrodites!). This can be caused both by aneuploidy for sex chromosomes in gametes, and by various disorders (for example, hormonal) in the process of sex differentiation.
An autosome is any of a pair of chromosomes that are identical in heterosexual individuals of the same species. In humans, there are 22 pairs of autosomes and one pair of sex chromosomes - X and Y. Each autosome in humans has a serial number in accordance with its size. The first is the largest, and the last is the shortest, carrying the fewest genes.
Chromosome types
Autosomal DNA is a term used in genetic genealogy to describe DNA that is inherited from autosomal chromosomes. An autosome is any chromosome that does not determine sex, so most chromosomes are autosomes. What is a chromosome, really? Chromosomes are made up of DNA and contain genes or units of heredity. Some organisms, like bacteria, have round chromosomes. However, in most organisms that have a nucleus in their cells, the chromosomes are straight or linear.
Humans and many animals have two types of chromosomes: autosomes and sex chromosomes. The sex chromosomes are those that are needed to determine the sex (male or female) of a person. Autosomes are all other chromosomes that are not needed for sex determination.
How many autosomes does a person have?
Humans have a total of 46 chromosomes in every cell of the body, of which 44 are autosomes. Each child gets one set (22 autosomes) from mom and another set (22 autosomes) from your dad. It's often easier to think of our autosomes in pairs because even though we have 44 autosomes, we actually only have 22 types. We have two copies of each type of autosome, one from each parent. Homologous chromosomes are two chromosomes of the same type that are the same size and shape and have identical genes.
The picture of all human chromosomes shows what each chromosome looks like. Autosomes are labeled with numbers. The sex chromosomes are outside the common row, they are assigned the letters X and Y. The image above is a karyogram from a male, because males have one X and one Y, while females have two X chromosomes.
Our paired autosomes are numbered from 1 to 22. They are numbered according to size so that chromosome 1 will be the longest and chromosome 22 will be the shortest. Homologous chromosomes are located next to each other. For example, both copies of chromosome 1 are located side by side.
Main groups
All body chromosomes are divided into two main groups based on function.
- In biology, autosomes are somatic chromosomes that carry only genetic somatic features.
- The sex chromosomes are one pair of chromosomes that help in sex determination.
There are 23 pairs (46) of chromosomes in a human. Of these, 22 pairs are autosomes, and one pair is called an allosome (sex chromosome). For a man it looks like 44 + XY, for a woman it looks like 44+ XX. Unlike prokaryotic cells, eukaryotic cells have many chromosomes into which they package their DNA. This allows eukaryotes to store much more genetic information.
Most eukaryotic organisms reproduce through sexual reproduction, which means that each individual has two copies of each chromosome. One copy is inherited from one parent, and the other copy is inherited from the other parent. This system increases genetic diversity and protects against certain diseases in that it allows individuals to inherit immune system genes from 2 different parents and have 2 copies of the gene.
It is normal for diploid eukaryotic organisms (having a complete set of chromosomes inherited through sexual reproduction) to have two copies of each autosome. Sex chromosomes are considered separate from autosomes, as their inheritance pattern works differently. The result is a unique set of chromosomes from both of the individual's parents. The genetic profile will include the DNA of each of his four grandparents.
Errors in the distribution of chromosomes
If errors occur during meiosis or at the beginning of embryonic development, serious diseases can develop in the body of a person who has the wrong number of chromosomes. Each chromosome contains thousands of genes, too many or too few chromosomes can lead to a serious imbalance in gene expression. Errors in chromosome replication can cause Down syndrome, which is caused by inheriting an extra copy of chromosome 21 from one parent.
Autosome Functions
Each autosome is a place where many thousands of genes are stored, each of which performs a unique function in the body's cells. Under normal circumstances, each chromosome follows a route that is common to individuals of a species. This allows the cells to know where to begin gene expression when they want to express a particular gene.
It is believed that factors that influence gene expression use this "map" to accurately respond to the needs of the cell. When autosomes are healthy, this allows the cell to perform an impressive array of functions. Each of the hundreds of subtly different cell types in a eukaryotic organism expresses a different combination of genes in the right place at the right time, performing a vast array of cellular functions.
All other chromosomes in dioecious organisms will be autosomes. The presence, number of copies, and structure of autosomes do not depend on the sex of a given eukaryotic organism.
Autosomes are designated by serial numbers. So, a person in the diploid set has 46 chromosomes, of which 44 autosomes (22 pairs, denoted by numbers from 1 to 22) and one pair of sex chromosomes (XX for women and XY for men).
Autosomal diseases
Autosomal dominant diseases are often inherited from affected parents to their children, having a family character. A child born from a heterozygous carrier of a dominant mutation (if the second parent does not have a similar genetic disorder) will have a 50% chance of being sick.
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Notes
Literature
- Griffiths Anthony J.F.. - New York: W.H. Freeman, 1999. - ISBN 071673771X.
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An excerpt characterizing the Autosome
“Ah, ma bonne, ma bonne, [Ah, dear, dear.],” he said, standing up and taking both of her hands. He sighed and added, “Le sort de mon fils est en vos mains.” Decidez, ma bonne, ma chere, ma douee Marieie qui j "ai toujours aimee, comme ma fille. [The fate of my son is in your hands. Decide, my dear, my dear, my meek Marie, whom I have always loved like a daughter. ]He went out. A real tear appeared in his eyes.
“Fr… fr…” snorted Prince Nikolai Andreevich.
- The prince, on behalf of his pupil ... son, makes a proposition for you. Do you want or not to be the wife of Prince Anatole Kuragin? You say yes or no! he shouted, “and then I reserve the right to say my opinion. Yes, my opinion and only my own opinion, ”added Prince Nikolai Andreevich, turning to Prince Vasily and answering his imploring expression. - Yes or no?
“My desire, mon pere, is never to leave you, never to share my life with yours. I don’t want to get married,” she said resolutely, looking with her beautiful eyes at Prince Vasily and at her father.
- Nonsense, nonsense! Nonsense, nonsense, nonsense! Prince Nikolai Andreevich shouted, frowning, took his daughter by the hand, bent her to him and did not kiss, but only bending his forehead to her forehead, touched her and squeezed the hand he was holding so that she winced and screamed.
Prince Vasily got up.
- Ma chere, je vous dirai, que c "est un moment que je n" oublrai jamais, jamais; mais, ma bonne, est ce que vous ne nous donnerez pas un peu d "esperance de toucher ce coeur si bon, si genereux. Dites, que peut etre ... L" avenir est si grand. Dites: peut etre. [My dear, I will tell you that I will never forget this moment, but, my kindest, give us at least a small hope of being able to touch this heart, so kind and generous. Say: maybe... The future is so great. Say maybe.]
- Prince, what I said is everything that is in my heart. I thank you for the honor, but I will never be your son's wife.
“Well, it’s over, my dear. Very glad to see you, very glad to see you. Come to yourself, princess, come, - he said old prince. “Very, very glad to see you,” he repeated, embracing Prince Vasily.
“My vocation is different,” Princess Marya thought to herself, my vocation is to be happy with another happiness, the happiness of love and self-sacrifice. And whatever it costs me, I will make poor Ame happy. She loves him so passionately. She repents so passionately. I will do everything to arrange her marriage to him. If he is not rich, I will give her money, I will ask my father, I will ask Andrey. I will be so happy when she is his wife. She is so unhappy, a stranger, lonely, without help! And my God, how passionately she loves, if she could so forget herself. Perhaps I would have done the same!…” thought Princess Mary.
