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
Books
- 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.
Scientists have been studying this topic for several decades. In recent years, they have begun to pay especially close attention to it. But the question that science is trying to answer still sounds fantastic: “Will men as a race die out?”
What exactly prompted Western geneticists and biologists to take up this problem cannot be answered unequivocally. The main version is this: men catastrophically quickly lose their reproductive function. Indeed, according to various estimates, 15-20% of the male population of the Earth are physiologically incapable of leaving offspring. It is also known that some scientists have asked the question: “What is happening to men?” while trying to solve another problem: to understand what is causing the surge in sexual violence in different parts of the planet. You don’t have to be too observant to notice: violence is basically the “occupation” of the “strong half” of humanity. There are other, no less “popular” now “same-sex” deviations, the reasons for which scientists are trying to figure out.
The male chromosome is defective by definition
Doctor of Biological Sciences Irina Vladimirovna ERMAKOVA, an employee of one of the institutes of the Russian Academy of Sciences, took up the problem of the development of biological characteristics of men and women in the mid-90s. It was then that the first publications of research on the degradation of the male sex chromosome appeared in the Western scientific press. Apparently, in Russia, Ermakova was one of the first scientists who undertook to analyze the topic of why the degradation of the male sex chromosome occurs.
In principle, any medical student is ready to answer this question: every person has 23 pairs of chromosomes. Each chromosome is a specific “chain” of genes. And only the last, 23rd, pair of chromosomes determines the sex of a person. What's new here?
“Indeed, this is basic knowledge,” says Irina Ermakova. — Females have two X chromosomes in the last pair. A man, in the last, 23rd pair, has one X chromosome, like a female individual, and the second is purely male, Y. Being paired, the XX chromosomes have the ability to duplicate each other. The XY combination indicates that complete interchangeability of chromosomes is impossible. Consequently, initially a woman, from a genetic point of view, is more stable.
Something else is known for certain. The male Y chromosome contains many of the same genes as the X chromosome. But the male Y has its own characteristics. It has two parts. The first, recombinant, is capable of exchanging genes with the X chromosome. This is why, for example, boys can look like grandmothers, and granddaughters can look like grandfathers. The non-recombinant part is unique, irreplaceable and carries exclusively “male” information. Modern science has proven that the Y chromosome is capable of destruction. It is the recombinant part of it that disappears, which has the ability to exchange information with another X chromosome. Moreover, this destruction is happening at a fairly rapid pace.
How fast? World-renowned geneticist and Oxford professor Brian Syke, who calls the male chromosome a “garbage bin” and “an archive of nature’s failed genetic experiments,” believes that men have 125,000 years left. Does the Y chromosome deserve this treatment? Alas, yes.
“Modern science has proven,” continues Irina Ermakova, “that the female X chromosome is inherited from mother and daughter and son, and from father only to daughters.” While the Y chromosome can only be passed on from father to son. Why? The X chromosome appeared first.
"Eve" came first?
Research conducted on the analysis of the bone remains of ancient people allowed scientists to conclude: the female X chromosome is older than the male Y by about 80-100 thousand years.
How was the research conducted?
Irina ERMAKOVA:
— In the 80s of the last century, geneticists from the University of California compared mitochondrial DNA in 147 people from Europe, Africa, Asia, Australia and New Guinea. The greatest DNA diversity was found in East Africa. This, by the way, indicates the African “roots” of modern man. We analyzed the mutations accumulated in the DNA of different people. According to the findings of the researchers, the common ancestor, to which all types of mtDNA of modern people go back, lived in East Africa about 200 thousand years ago. She was conventionally called “mitochondrial Eve”. Mitochondrial Eve had many thousands of fellow tribesmen, but their mtDNA has not reached us. Analysis of mitochondrial DNA and the Y chromosome on archaeological material showed that the X chromosome is much older (about 20 thousand years - 80 thousand years) than the Y chromosome. It has been suggested that, most likely, the Y chromosome is a modified X.
Indeed, most modern studies agree on one thing: in the process of evolution, under the influence of external factors, certain genes were actively modified. Everyone also agrees that the male Y chromosome is the result of unknown mutations on the female X chromosome. But how then did they become fruitful and multiply in a lovely female society?
Proponents of one of the many theories make us understand that in the beginning there was parthenogenesis. In other words, this is a form of sexual reproduction in which female reproductive cells develop without fertilization. And full-fledged sex chromosomes appeared later: in animals and, consequently, in humans. Because animals and people themselves appeared later. And the distant ancestors of mammals engaged in parthenogenesis.
Who was "Eva"?
Having analyzed several dozen different works, Irina Ermakova suggests drawing different conclusions:
— There is a hypothesis that there was originally a kingdom of females on Earth, including humans.
The impetus for the emergence of a hypothesis about the female origin of humanity was given to many scientists by the study of ancient rock paintings. They are replete with images of hermaphrodites: creatures similar to humans, simultaneously with female breasts and a male penis. It can be assumed that initially there were hermaphrodite women on Earth who were capable of both fertilizing an egg and giving birth. Reproduction occurred as a result of contact between two hermaphrodite females.
Hermaphrodite women were distinguished by the presence of two active X chromosomes. In today's women, only one X chromosome is active, the other is passive. Perhaps it was mutations and gene destruction in one of the X chromosomes in ancient times that could lead to the fact that some hermaphrodite women with an altered chromosome were no longer capable of childbearing. After all, today it is known that even small changes in sex chromosomes can lead to infertility.
The barren began to serve as protectors and hunters. And real hermaphrodite women preferred them as partners: after all, such women could help raise children, provide food, and protect. Such partners can conventionally be called “Amazon” women. What is a good huntress? This is strength, calculation and lack of emotion. Quite traditional male virtues. In the process of evolution, the female sex hormone began to change.
Another evidence of the origin of men from hermaphrodite women is the presence of nipples on their chests. By the way, during the experiments, male rats, after injecting them with female sex hormones and lactogenic hormone, began to secrete milk!
Well... Cases of men secreting milk, without any scientific experiments, were also mentioned by the authors of the Brockhaus and Efron dictionary.
One way or another, modern researchers believe that the appearance of the male Y chromosome is associated with changes in one of the female X chromosomes. The reasons are evolutionary selection and external, natural factors.
What's happened "female brains"?
“The complete disappearance of some genes and the appearance of new genes as a result of mutation,” says Irina Ermakova, “led to the formation of a new hormone, later called the male sex hormone. Indeed, the male sex hormone testosterone is very similar to the female one, estradiol. But they act on the body differently. First, testosterone enhances muscularity. Secondly, testosterone and estradiol, which are synthesized in different proportions in both men and women, have different effects on the functioning of the human brain. The male hormone activates the left hemisphere and suppresses the activity of the right. The female one activates the work of both hemispheres, with a slight predominance towards the right.
The left and right hemispheres have different functional meanings. The left hemisphere is analysis, logic, abstract thinking, sequential processing of information. The right is responsible for emotional and holistic perception, synthesis, intuition.
Scientists have found that women's brains have significantly more connections between the left and right hemispheres than men's brains. This makes women more resilient. For example, if a man has a stroke in the left hemisphere, then he is doomed. On the right - he survives. It’s different for a woman: in any case, she will survive at the expense of the other hemisphere.
Seraphim BERESTOV
Genetic research of the human body is one of the most necessary for the population of the entire planet. It is genetics that is of great importance for studying the causes of hereditary diseases or predisposition to them. We'll tell you how many chromosomes does a person have, and what this information may be useful for.
How many pairs of chromosomes does a person have?
The cell of the body is designed to store, implement and transmit hereditary information. It is created from a DNA molecule and is called a chromosome. Many people are interested in the question of how many pairs of chromosomes a person has.
Humans have 23 pairs of chromosomes. Until 1955, scientists erroneously calculated the number of chromosomes to be 48, i.e. 24 pairs. The error was discovered by scientists using more precise techniques.
The set of chromosomes is different in somatic and germ cells. The doubled (diploid) set is present only in the cells that determine the structure (somatics) of the human body. One part is of maternal origin, the other part is of paternal origin.
Gonosomes (sex chromosomes) have only one pair. They differ in gene composition. Therefore, depending on gender, a person has a different composition of the pair of gonosomes. From the fact how many chromosomes do women have, The gender of the unborn child does not depend. A woman has a set of XX chromosomes. Its reproductive cells do not influence the development of sexual characteristics during fertilization of the egg. Belonging to a particular gender depends on the information code about how many chromosomes does a man have. It is the difference between the XX and XY chromosomes that determines the sex of the unborn child. The remaining 22 pairs of chromosomes are called autosomal, i.e. the same for both sexes.
- A woman has 22 pairs of autosomal chromosomes and one pair XX;
- A man has 22 pairs of autosomal chromosomes and one XY pair.
The structure of chromosomes changes during division in the process of doubling somatic cells. These cells are constantly dividing, but the set of 23 pairs has a constant value. The structure of chromosomes is influenced by DNA. The genes that make up the chromosomes form a specific code under the influence of DNA. Thus, the information obtained during the DNA coding process determines the individual characteristics of a person.
Changes in the quantitative structure of chromosomes
A person's karyotype determines the totality of chromosomes. Sometimes it can be modified due to chemical or physical reasons. The normal number of 23 chromosomes in somatic cells can vary. This process is called aneuploidy.
- The number may be less, then this is monosomy.
- If there is no pair of autotenous cells, then this structure is called nullisomy.
- If a third chromosome is added to a pair of cells that make up a chromosome, then this is trisomy.
Various changes in the quantitative set lead to a person receiving congenital diseases. Abnormalities in the structure of chromosomes cause Down syndrome, Edwards syndrome and other conditions.
There is also a variation called polyploidy. With this deviation, a multiple increase in chromosomes occurs, that is, a doubling of a pair of cells that is part of one chromosome. A diploid or germ cell can be present three times (triploidy). If it is present 4 or 5 times, then this increase is called tetraploidy and pentaploidy, respectively. If a person has such a deviation, then he dies within the first days of life. The plant world is quite widely represented by polyploidy. A multiple increase in chromosomes is present in animals: invertebrates, fish. Birds with this anomaly die.
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B chromosomes have not yet been discovered in humans. But sometimes an additional set of chromosomes appears in cells - then they talk about polyploidy, and if their number is not a multiple of 23 - about aneuploidy. Polyploidy occurs in certain types of cells and contributes to their increased work, while aneuploidy usually indicates disturbances in the functioning of the cell and often leads to its death.
We must share honestly
Most often, an incorrect number of chromosomes is a consequence of unsuccessful cell division. In somatic cells, after DNA duplication, the maternal chromosome and its copy are linked together by cohesin proteins. Then kinetochore protein complexes sit on their central parts, to which microtubules are later attached. When dividing along microtubules, kinetochores move to different poles of the cell and pull chromosomes with them. If the crosslinks between copies of a chromosome are destroyed ahead of time, then microtubules from the same pole can attach to them, and then one of the daughter cells will receive an extra chromosome, and the second will remain deprived.
Meiosis also often goes wrong. The problem is that the structure of linked two pairs of homologous chromosomes can twist in space or separate in the wrong places. The result will again be an uneven distribution of chromosomes. Sometimes the reproductive cell manages to track this so as not to pass the defect on to inheritance. The extra chromosomes are often misfolded or broken, which triggers the death program. For example, among spermatozoa there is such selection for quality. But the eggs are not so lucky. All of them are formed in humans even before birth, prepare for division, and then freeze. The chromosomes have already been duplicated, tetrads have been formed, and division has been delayed. They live in this form until the reproductive period. Then the eggs mature in turn, divide for the first time and freeze again. The second division occurs immediately after fertilization. And at this stage it is already difficult to control the quality of division. And the risks are greater, because the four chromosomes in the egg remain cross-linked for decades. During this time, damage accumulates in cohesins, and chromosomes can spontaneously separate. Therefore, the older the woman, the greater the likelihood of incorrect chromosome segregation in the egg.
Aneuploidy in germ cells inevitably leads to aneuploidy of the embryo. If a healthy egg with 23 chromosomes is fertilized by a sperm with extra or missing chromosomes (or vice versa), the number of chromosomes in the zygote will obviously be different from 46. But even if the sex cells are healthy, this does not guarantee healthy development. In the first days after fertilization, embryonic cells actively divide in order to quickly gain cell mass. Apparently, during rapid divisions there is no time to check the correctness of chromosome segregation, so aneuploid cells can arise. And if an error occurs, then the further fate of the embryo depends on the division in which it happened. If the balance is disturbed already in the first division of the zygote, then the entire organism will grow aneuploid. If the problem arose later, then the outcome is determined by the ratio of healthy and abnormal cells.
Some of the latter may continue to die, and we will never know about their existence. Or he can take part in the development of the organism, and then it will turn out mosaic- different cells will carry different genetic material. Mosaicism causes a lot of trouble for prenatal diagnosticians. For example, if there is a risk of having a child with Down syndrome, sometimes one or more cells of the embryo are removed (at a stage when this should not pose a danger) and the chromosomes in them are counted. But if the embryo is mosaic, then this method becomes not particularly effective.
Third wheel
All cases of aneuploidy are logically divided into two groups: deficiency and excess of chromosomes. The problems that arise with a deficiency are quite expected: minus one chromosome means minus hundreds of genes.
If the homologous chromosome works normally, then the cell can get away with only an insufficient amount of the proteins encoded there. But if some of the genes remaining on the homologous chromosome do not work, then the corresponding proteins will not appear in the cell at all.
In the case of an excess of chromosomes, everything is not so obvious. There are more genes, but here - alas - more does not mean better.
Firstly, excess genetic material increases the load on the nucleus: an additional strand of DNA must be placed in the nucleus and served by information reading systems.
Scientists have discovered that in people with Down syndrome, whose cells carry an extra 21st chromosome, the functioning of genes located on other chromosomes is mainly disrupted. Apparently, an excess of DNA in the nucleus leads to the fact that there are not enough proteins to support the functioning of chromosomes for everyone.
Secondly, the balance in the amount of cellular proteins is disrupted. For example, if activator proteins and inhibitor proteins are responsible for some process in a cell, and their ratio usually depends on external signals, then an additional dose of one or the other will cause the cell to stop responding adequately to the external signal. Finally, an aneuploid cell has an increased chance of dying. When DNA is duplicated before division, errors inevitably occur, and the cellular repair system proteins recognize them, repair them, and start doubling again. If there are too many chromosomes, then there are not enough proteins, errors accumulate and apoptosis is triggered - programmed cell death. But even if the cell does not die and divides, then the result of such division will also most likely be aneuploids.
You will live
If even within one cell aneuploidy is fraught with malfunctions and death, then it is not surprising that it is not easy for an entire aneuploid organism to survive. At the moment, only three autosomes are known - 13, 18 and 21, trisomy for which (that is, an extra third chromosome in cells) is somehow compatible with life. This is likely due to the fact that they are the smallest and carry the fewest genes. At the same time, children with trisomy on the 13th (Patau syndrome) and 18th (Edwards syndrome) chromosomes live at best up to 10 years, and more often live less than a year. And only trisomy on the smallest chromosome in the genome, the 21st chromosome, known as Down syndrome, allows you to live up to 60 years.
People with general polyploidy are very rare. Normally, polyploid cells (carrying not two, but from four to 128 sets of chromosomes) can be found in the human body, for example, in the liver or red bone marrow. These are usually large cells with enhanced protein synthesis that do not require active division.
An additional set of chromosomes complicates the task of their distribution among daughter cells, so polyploid embryos, as a rule, do not survive. Nevertheless, about 10 cases have been described in which children with 92 chromosomes (tetraploids) were born and lived from several hours to several years. However, as in the case of other chromosomal abnormalities, they lagged behind in development, including mental development. However, many people with genetic abnormalities come to the aid of mosaicism. If the anomaly has already developed during the fragmentation of the embryo, then a certain number of cells may remain healthy. In such cases, the severity of symptoms decreases and life expectancy increases.
Gender injustices
However, there are also chromosomes, the increase in the number of which is compatible with human life or even goes unnoticed. And these, surprisingly, are sex chromosomes. The reason for this is gender injustice: approximately half of the people in our population (girls) have twice as many X chromosomes as others (boys). At the same time, the X chromosomes not only serve to determine sex, but also carry more than 800 genes (that is, twice as many as the extra 21st chromosome, which causes a lot of trouble for the body). But girls come to the aid of a natural mechanism for eliminating inequality: one of the X chromosomes is inactivated, twists and turns into a Barr body. In most cases, the choice occurs randomly, and in some cells the result is that the maternal X chromosome is active, while in others the paternal one is active. Thus, all girls turn out to be mosaic, because different copies of genes work in different cells. A classic example of such mosaicism is tortoiseshell cats: on their X chromosome there is a gene responsible for melanin (a pigment that determines, among other things, coat color). Different copies work in different cells, so the coloring is spotty and is not inherited, since inactivation occurs randomly.
As a result of inactivation, only one X chromosome always works in human cells. This mechanism allows you to avoid serious troubles with X-trisomy (XXX girls) and Shereshevsky-Turner syndrome (XO girls) or Klinefelter (XXY boys). About one in 400 children is born this way, but vital functions in these cases are usually not significantly impaired, and even infertility does not always occur. It is more difficult for those who have more than three chromosomes. This usually means that the chromosomes did not separate twice during the formation of sex cells. Cases of tetrasomy (ХХХХ, ХХYY, ХХХY, XYYY) and pentasomy (XXXXX, XXXXY, XXXYY, XXYYY, XYYYY) are rare, some of them have been described only a few times in the history of medicine. All of these options are compatible with life, and people often live to an advanced age, with abnormalities manifested in abnormal skeletal development, genital defects, and decreased mental abilities. Typically, the additional Y chromosome itself does not significantly affect the functioning of the body. Many men with the XYY genotype do not even know about their peculiarity. This is due to the fact that the Y chromosome is much smaller than the X and carries almost no genes that affect viability.
Sex chromosomes have another interesting feature. Many mutations of genes located on autosomes lead to abnormalities in the functioning of many tissues and organs. At the same time, most gene mutations on sex chromosomes manifest themselves only in impaired mental activity. It turns out that sex chromosomes largely control brain development. Based on this, some scientists hypothesize that they are responsible for the differences (however, not fully confirmed) between the mental abilities of men and women.
Who benefits from being wrong?
Despite the fact that medicine has been familiar with chromosomal abnormalities for a long time, recently aneuploidy continues to attract the attention of scientists. It turned out that more than 80% of tumor cells contain an unusual number of chromosomes. On the one hand, the reason for this may be the fact that proteins that control the quality of division are able to slow it down. In tumor cells, these same control proteins often mutate, so restrictions on division are lifted and chromosome checking does not work. On the other hand, scientists believe that this may serve as a factor in the selection of tumors for survival. According to this model, tumor cells first become polyploid, and then, as a result of division errors, they lose different chromosomes or parts thereof. This results in a whole population of cells with a wide variety of chromosomal abnormalities. Most are not viable, but some may succeed by chance, for example if they accidentally gain extra copies of genes that trigger division or lose genes that suppress it. However, if the accumulation of errors during division is further stimulated, the cells will not survive. The action of taxol, a common cancer drug, is based on this principle: it causes systemic chromosome nondisjunction in tumor cells, which should trigger their programmed death.
It turns out that each of us may be a carrier of extra chromosomes, at least in individual cells. However, modern science continues to develop strategies to deal with these unwanted passengers. One of them suggests using proteins responsible for the X chromosome and targeting, for example, the extra 21st chromosome of people with Down syndrome. It is reported that this mechanism was brought into action in cell cultures. So, perhaps, in the foreseeable future, dangerous extra chromosomes will be tamed and rendered harmless.
