Human chromosomes. See what “8th human chromosome” is in other dictionaries Brief genetic information

Idiogram of the 2nd human chromosome. The 2nd human chromosome is one of 23 human chromosomes and the second largest, one of 22 human autosomes. The chromosome contains more than 242 million base pairs... Wikipedia

Idiogram of the 22nd human chromosome The 22nd human chromosome is one of 23 human chromosomes, one of 22 autosomes and one of 5 acrocentric human chromosomes. The chromosome contains o... Wikipedia

Idiogram of the 11th human chromosome. The 11th human chromosome is one of 23 pairs of human chromosomes. The chromosome contains almost 139 million base pairs... Wikipedia

Idiogram of human chromosome 12. Human chromosome 12 is one of 23 human chromosomes. The chromosome contains almost 134 million base pairs... Wikipedia

Idiogram of the 21st human chromosome The 21st human chromosome is one of 23 human chromosomes (in the haploid set), one of 22 autosomes and one of 5 acrocentric human chromosomes. The chromosome contains about 48 million base pairs, which ... Wikipedia

Idiogram of the 7th human chromosome. The 7th human chromosome is one of 23 human chromosomes. The chromosome contains more than 158 million base pairs, which is from 5 to 5.5% ... Wikipedia

Idiogram of the 1st human chromosome. The 1st human chromosome is the largest of the 23 human chromosomes, one of the 22 human autosomes. The chromosome contains about 248 million base pairs... Wikipedia

Idiogram of the 3rd human chromosome. The 3rd human chromosome is one of 23 human chromosomes, one of 22 human autosomes. The chromosome contains almost 200 million base pairs... Wikipedia

Idiogram of the 9th human chromosome. The 9th human chromosome is one of the chromosomes of the human genome. Contains about 145 million base pairs, making up 4% to 4.5% of all cellular DNA material. According to different estimates... Wikipedia

Idiogram of human chromosome 13. Human chromosome 13 is one of 23 human chromosomes. The chromosome contains more than 115 million base pairs, which is from 3.5 to 4% of the total material ... Wikipedia

Idiogram of the 14th human chromosome. The 14th human chromosome is one of 23 human chromosomes. The chromosome contains approximately 107 million base pairs, which is from 3 to 3.5% of the total material ... Wikipedia

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• Telomere effect. A Revolutionary Approach to Living Younger, Healthier, Longer, Elizabeth Helen Blackburn, Elissa Epel. What is this book about? For life to continue, the cells of the body must continuously divide, creating their exact copies - young and full of energy. They, in turn, also begin to share. So…

Today society is constantly evolving. It would seem that technology in the 21st century should have made life much easier for people. In pursuit of the benefits of civilization and stereotypes of being successful, our body is constantly exposed to harmful effects. We are talking about lack of sleep, quick snacks of unhealthy food, stress and depression against the background of chronic fatigue. All these factors directly affect a person’s ability to conceive physically and mentally developed offspring.

According to statistics, today about 4% of children are born with various genetic disorders. Doctors diagnose 40% of newborns with mental disabilities. What is the reason? According to doctors and scientists, it's all about the genome. In our article we will try to understand mutations at this level. We will also tell you how many chromosome pairs people should have normally, which affects their number.

Brief genetic information

First you need to understand the issues of genetics. Without appropriate specialized education, it is difficult to say at first glance how many pairs of chromosomes a person has and what they are. In simple terms, it is a cell or element of an organism. The main function of a chromosome is to store and transmit the genetic code that was originally contained in it.

It consists of proteins (63%) and nucleic acids (DNA). Cytogenetics studies chromosomes. Experts in this field have long proven that it is acids that are responsible for the hereditary transmission of information. During cell division, they determine the baby's gender, eye color and hair structure, as well as the shade of the skin. They also bear responsibility for the future health of the child. It is almost impossible to find out exactly which genes will be passed on to the baby before it is born. The thing is that the laying of hereditary information occurs at the moment of conception.

Formation of the genotype

How many pairs of chromosomes does a healthy person have? There are 23 of them in total, and they do not change throughout life. Some diseases are characterized by an increase in this amount. A striking example of such transformations is Down syndrome. Each chromosome is responsible for the gene that was originally assigned to it. One is passed down from the father, and the other from the mother. Affected people have 47 chromosomes. The main reason for such disorders lies in the unhealthy genome of the parents.

A karyotype is usually understood as a sign of high-quality as well as low-quality chromosomes. It is considered within one cellular element. Any abnormalities in the genome determine the severity of the disease or its absence. Thanks to the development of medicine, today, with the help of a special analysis, it is possible to determine whether the baby has anomalies even before the baby is born.

Probable deviations in the karyotype

The studied karyotypic disorders are usually divided into two categories:

• Genetic (increase in the total number or number of chromosomes in one of the pairs).
• Chromosomal (rearrangement of cells and pairs, which affects the quality of the gene material).

With obvious deviations in the karyotype, not only the structure, but also the location and qualitative characteristics of the chromosomes can change. Next, let's look at how many pairs of chromosomes people can have for various disorders, and what diseases they are talking about.

Down syndrome

The first descriptions of pathology date back to the 17th century. However, at that time it was not yet known exactly how many pairs of chromosomes people should have normally. According to statistics, today for every thousand newborns there are two children with this syndrome. The main reason for its development is a deviation in the genome due to diabetic disease in the parents or late conception. To the 21 pairs of elements carrying hereditary information, another one is added. Answering the question about how many pairs of chromosomes a Down person has, we get the number 47.

Children with this syndrome differ from healthy peers in appearance. Among the main manifestations of pathology are:

People with this pathology rarely live past 50 years of age because they have other physical abnormalities. For example, men are unable to conceive a child. They have deviations in the development of the genital organs. Women can take on the role of mother, but there is a high probability of having children with the same disease.

Today, with the help of special genetic tests, you can find out this insidious diagnosis even during pregnancy. If the analysis confirms the pathology, the woman is offered an abortion. However, the final decision remains with the parents. Many couples, knowing about the diagnosis, do not agree to an artificial termination of pregnancy.

Patau syndrome

With this disease, mutations affect the twentieth chromosome, as a result of which an extra pair is added to it. The likelihood of a child being born with a disorder is negligible - for every 5 thousand babies there are 1-2% of deviations.

The disease is diagnosed in the first days of life. Using special tests, you can understand how many pairs of chromosomes there are per person. As the baby grows, symptoms characteristic of the syndrome appear:

• more than 10 fingers/toes;
• eye shape is too small;
• clefts in the palate or lips.

The mortality rate of children with Patau syndrome is extremely high. They rarely live to be 3-4 years old, since multiple developmental defects interfere with normal existence.

Edwards syndrome

With this pathology, an extra pair is added to the eighteenth chromosome. Shortly after birth, children with Edwards syndrome die from various causes. Developmental disorders do not allow the baby to eat properly and absorb the food he receives. If the child survives, he is usually diagnosed with muscle wasting. Externally, the disease manifests itself as too low-set ears, wide-set eyes and other physical abnormalities.

Let's sum it up

How many pairs of chromosomes does a person normally have? There should be 23 of them. For any deviations from this indicator, the child is born with various developmental defects. Therefore, doctors strongly recommend that both parents consult a geneticist before conceiving. This is especially true for those married couples who already have a history of cases of the pathologies listed above.

People whose age at the time of conception is 35 years or more are also at risk. They are recommended not only to undergo a comprehensive examination before planning a baby, but also to be observed by qualified specialists throughout the pregnancy. Only in this case can one hope for a favorable outcome, the birth of a healthy child. And the question “how many pairs of chromosomes should people have normally” will not worry parents.

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

We propose to look into this issue in order to dot the i’s once and for all.

Looking at family photographs, you may have probably noticed that members of the same family resemble each other: children look like parents, parents look like grandparents. This similarity is passed on from generation to generation through amazing mechanisms.

All living organisms, from single-celled organisms to African elephants, contain chromosomes in the cell nucleus - thin, long threads that can only be seen with 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, implement it and transmit it.

How many chromosomes does a person have

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

For example, peas have 14 chromosomes, y have 42, and in humans – 46 (that is, 23 pairs). Hence the temptation arises to conclude that the more there are, the more complex the creature that possesses them. However, in reality this is absolutely not the case.

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

In a female organism, a pair of gonosomes contains two X chromosomes (XX-pair), and in a male organism, one X-chromosome 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 the 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 (deoxyribonucleic acid) molecule, similar to a double helix. Each cell contains about 2 meters of DNA, and in total there are about 100 billion km of DNA in the cells of our body.

An interesting fact is that if there is an extra chromosome or if at least one of the 46 is missing, a person experiences a mutation and serious developmental abnormalities (Down's disease, etc.).

The subject of genetic research is the phenomena of heredity and variability. American scientist T-H. Morgan created the chromosomal theory of heredity, which proves that each biological species can be characterized by a specific karyotype, which contains such types of chromosomes as somatic and sex chromosomes. The latter are represented by a separate pair, distinguished by male and female individuals. In this article we will study what structure female and male chromosomes have and how they differ from each other.

What is a karyotype?

Each cell containing a nucleus is characterized by a certain number of chromosomes. It is called a karyotype. In different biological species, the presence of structural units of heredity is strictly specific, for example, the human karyotype is 46 chromosomes, chimpanzees - 48, crayfish - 112. Their structure, size, shape differ in individuals belonging to different systematic taxa.

The number of chromosomes in a body cell is called the diploid set. It is characteristic of somatic organs and tissues. If as a result of mutations the karyotype changes (for example, in patients with Klinefelter syndrome the number of chromosomes is 47, 48), then such individuals have reduced fertility and in most cases are infertile. Another hereditary disease associated with sex chromosomes is Turner-Shereshevsky syndrome. It occurs in women who have 45 rather than 46 chromosomes in their karyotype. This means that in a sexual pair there are not two X chromosomes, but only one. Phenotypically, this manifests itself in underdevelopment of the gonads, weakly expressed secondary sexual characteristics and infertility.

Somatic and sex chromosomes

They differ both in shape and in the set of genes that make up them. The male chromosomes of humans and mammals are included in the heterogametic sexual pair XY, which ensures the development of both primary and secondary male sexual characteristics.

In male birds, the sexual pair contains two identical ZZ male chromosomes and is called homogametic. Unlike chromosomes that determine the sex of an organism, the karyotype contains hereditary structures that are identical in both males and females. They are called autosomes. There are 22 pairs of them in the human karyotype. Sexual male and female chromosomes form 23 pairs, so a man’s karyotype can be represented as a general formula: 22 pairs of autosomes + XY, and women - 22 pairs of autosomes + XX.

Meiosis

The formation of germ cells - gametes, the fusion of which forms a zygote, occurs in the sex glands: testes and ovaries. In their tissues, meiosis occurs - the process of cell division leading to the formation of gametes containing a haploid set of chromosomes.

Oogenesis in the ovaries leads to the maturation of eggs of only one type: 22 autosomes + X, and spermatogenesis ensures the maturation of two types of gomets: 22 autosomes + X or 22 autosomes + Y. In humans, the sex of the unborn child is determined at the moment of fusion of the nuclei of the egg and sperm and depends from the karyotype of the sperm.

Chromosomal mechanism and sex determination

We have already looked at the moment at which sex is determined in a person - at the moment of fertilization, and it depends on the chromosomal set of the sperm. In other animals, representatives of different sexes differ in the number of chromosomes. For example, in marine worms, insects, and grasshoppers, in the diploid set of males there is only one chromosome from the sexual pair, and in females - both. Thus, the haploid set of chromosomes of the male sea worm Acirocanthus can be expressed by the formulas: 5 chromosomes + 0 or 5 chromosomes + x, and females have only one set of 5 chromosomes + x in their eggs.

What influences sexual dimorphism?

In addition to chromosomal, there are other ways to determine sex. In some invertebrates - rotifers - sex is determined even before the fusion of gametes - fertilization, as a result of which male and female chromosomes form homologous pairs. Females of the marine polychaete Dinophyllus produce two types of eggs during oogenesis. The first ones are small, depleted in yolk, and males develop from them. Others - large, with a huge supply of nutrients - serve for the development of females. In honey bees - insects of the Hymenoptera series - females produce two types of eggs: diploid and haploid. From unfertilized eggs, males develop - drones, and from fertilized eggs - females, who are worker bees.

Hormones and their effect on gender formation

In humans, male glands - the testes - produce sex hormones such as testosterone. They influence both development (anatomical structure of the external and internal genital organs) and physiological features. Under the influence of testosterone, secondary sexual characteristics are formed - skeletal structure, figure features, body hair, timbre of voice. In a woman’s body, the ovaries produce not only sex cells, but also hormones, being Sex hormones, such as estradiol, progesterone, estrogen, contribute to the development of external and internal genital organs, female body hair, regulate the menstrual cycle and pregnancy.

In some vertebrates, fish, and amphibians, biologically active substances produced by the gonads strongly influence the development of primary and secondary sexual characteristics, but the types of chromosomes do not have such a great impact on the formation of sex. For example, the larvae of marine polychaetes - Bonellias - under the influence of female sex hormones stop their growth (size 1-3 mm) and become dwarf males. They live in the genital tract of females, which have a body length of up to 1 meter. In cleaner fish, males maintain harems of several females. Females, in addition to the ovaries, have the rudiments of the testes. As soon as the male dies, one of the harem females takes over his function (male gonads that produce sex hormones begin to actively develop in her body).

Sex regulation

It is carried out by two rules: the first determines the dependence of the development of the rudimentary gonads on the secretion of testosterone and the hormone MIS. The second rule indicates the exceptional role played by the Y chromosome. The male sex and all the anatomical and physiological characteristics corresponding to it develop under the influence of genes located on the Y chromosome. The interrelation and dependence of both rules in human genetics is called the principle of growth: in an embryo that is bisexual (that is, having the rudiments of the female glands - the Müllerian duct and the male gonads - the Wolffian canal), the differentiation of the embryonic gonad depends on the presence or absence of the Y chromosome in the karyotype.

Genetic information on the Y chromosome

Research by geneticists, in particular T-H. Morgan, it was found that in humans and mammals the gene composition of the X and Y chromosomes is not the same. Human male chromosomes lack some of the alleles present on the X chromosome. However, their gene pool contains the SRY gene, which controls spermatogenesis, leading to the formation of the male sex. Hereditary disturbances of this gene in the embryo lead to the development of a genetic disease - Swire's syndrome. As a result, the female individual developing from such an embryo contains in the XY karyotype a sexual pair or only a section of the Y chromosome containing the gene locus. It activates the development of gonads. In sick women, secondary sexual characteristics are not differentiated and they are infertile.

Y chromosome and hereditary diseases

As noted earlier, the male chromosome differs from the X chromosome both in size (it is smaller) and in shape (it looks like a hook). The set of genes is also specific to it. Thus, a mutation in one of the genes on the Y chromosome is phenotypically manifested by the appearance of a tuft of coarse hair on the earlobe. This sign is typical only for men. There is a known hereditary disease called Klinefelter syndrome. A sick man has extra female or male chromosomes in his karyotype: XXY or XXYY.

The main diagnostic signs are pathological growth of the mammary glands, osteoporosis, and infertility. The disease is quite common: for every 500 newborn boys, there is 1 patient.

To summarize, we note that in humans, as in other mammals, the sex of the future organism is determined at the moment of fertilization, due to a certain combination of sex X and Y chromosomes in the zygote.

There is a hypothesis that the male Y chromosome is a “defective” female X chromosome.
Photo by Washington University School of Medicine in St. Louis

This story began at least eight years ago.

Then, in 2004, Professor Jenny Graves from the Australian National University said at the 15th International Conference on Chromosomes, held at Brunel University, that in the next 10 million years, men as a biological subspecies may be on the verge of extinction. Graves based his evolutionary pessimism on the hypothesis he put forward: the “male” Y chromosome characteristic of mammals (the Y chromosome) would ultimately lose its several dozen genes. Including the famous SRY gene (the so-called “maleness” gene - Sex-determining Region of Y), which is responsible for the production of male hormones and spermatogenesis.

The fact is that it has been established quite accurately: at its origin, 300 million years ago, the Y chromosome contained 1438 genes; now, according to various estimates, from 45 to 82 (according to the latest data - 78). And this is compared to approximately 800 genes on the X chromosome (X chromosome)┘ Regression, as they say, is obvious! In general, there is an assumption that the Y chromosome is a “defective” female X chromosome.

Recall that the human genome consists of 23 pairs of chromosomes. Only in women, the 23rd pair consists of two X chromosomes, and in men, the Y chromosome was “adjoined” to the X chromosome 300 million years ago (due to what circumstances is a separate question). Since the Y chromosome does not have a pair, until recently it was believed that it was almost a “degrading dump” of genetic material. There was an opinion that the lack of ability to correct errors that occur leads to a gradual “switching off” of the genes on the Y chromosome.

“This small sex chromosome determines the male sex in humans,” noted Professor Vyacheslav Tarantul in his monograph “The Human Genome: An Encyclopedia Written in Four Letters” (M., 2003). “The sequences it contains are considered very young.” The mutation rate on this chromosome is four times higher than on chromosome X. Genes have been identified only on the left end of this chromosome (the right end has not yet been completely sequenced). According to the latest updated data, their maximum number does not even reach 100. On average, there are only five genes per 1 million letter-nucleotides.”

All this gave reason to Professor Brian Sykes, author of the 2003 book “Adam’s Curse: A Future Without Men,” to confidently predict the disappearance of men within 100 thousand years.

But it seems that this time it went through!

An article was published in one of the latest issues of the authoritative scientific journal Nature, which proves that the “degradation” of the Y chromosome has practically stopped. Jennifer Hughes and her colleagues at the Whitehead Institute in Cambridge, Massachusetts, studied the Y chromosome of rhesus monkeys, which are separated from humans by 25 million years of evolution.

The researchers came to the conclusion, the BBC reports, that over the past 6 million years, the degradation of the human Y chromosome has been minimal - it has not lost a single gene, and over a period of 25 million years, the number of genes has decreased by one.

“The Y chromosome is not going away and gene loss has virtually stopped,” Dr. Hughes explains. “We cannot rule out the possibility that this may happen in the future, but those genes that are present on the Y chromosome will remain with us. They appear to perform some critical function that we are still only guessing at, but these genes are well preserved through natural selection.”

But this is really the most intriguing question: why was such an “unfinished” chromosome needed in the genome of Homo sapiens? There are many possible answers to this question.

Today, for example, the connection between the genes of chromosome X and diseases such as Duchenne muscular dystrophy, breast cancer, prostate cancer, cardiomyopathy, epilepsy, hemophilia B has already been precisely established... A terrifying list, isn’t it! And this is only a small part of the 208 genes on the X chromosome associated with diseases. Only three disease-associated genes have been identified on the male Y chromosome.

Moreover, there is reason to believe that it was the emergence of the Y chromosome that played the main role in the origin of humans from ape-like ancestors. It is known, for example, that all mammals, including monkeys, have the same piece of DNA on the female sex chromosome X, about 4 million nucleotide sequences long. But only in modern humans this section of DNA was also copied onto the male Y chromosome. Perhaps this is the very hypothetical “human gene”.

Again, the smallest difference in the genomes of humans and chimpanzees is observed between the X chromosomes, and the largest - between the Y chromosomes. Although there are exceptions here: among the Bushmen of Southern and Eastern Africa, a mutation was identified in the Y chromosome, which is present in monkeys, but absent in populations of other people. Scientists suggest that this mutation arose before the evolutionary separation of humans and chimpanzees.

However, you can’t “overdo it” here either. There have been cases when human cells have not one, but two or even three copies of the Y chromosome. Characteristic signs of such a chromosomal pathology are antisocial behavior and various psychological disorders, characteristic of 35% of patients. A kind of genetically programmed macho for aggression┘

Be that as it may, it seems that it is the Y chromosome that plays the role of the source of evolutionary changes in humans. It is men who are responsible for many of the mutations that accumulate in the human genome. In other words, humanity, deprived of the male Y chromosome, will resemble a cutting-edge concept car that they forgot to put an engine in. But the Nature article seems to put an end to men's unmotivated anxiety about their evolutionary future.

At the very least, Professor Mark Pagel, whose opinion is quoted by the BBC, who deals with the problems of evolutionary biology at the University of Reading, believes that nothing threatens the future of men in the long term: “This paper convincingly shows that the loss of genes in the Y chromosome in the early stages of evolution occurs relatively quickly, but then reaches a point at which selection forces the process to stop.”

Well, well, we’re alive, guys!