How does the process of birth of men and women take place? The X and Y chromosomes are responsible for this. And it all begins when 400 million sperm rush to search for an egg. This is not such a difficult task as it might seem at first glance. IN human body The egg can be compared to a huge star, towards which small sperm star fighters are rushing from all sides.

Now let's talk about chromosomes. They contain all the information necessary for the creation of man. A total of 46 chromosomes are needed. They can be compared to 46 thick volumes of an encyclopedia. Each person receives 23 chromosomes from their mother, and the remaining 23 from their father. But only 2 are responsible for sex, and one must be the X chromosome.

If you get a set of 2 X chromosomes, you will use the women's restroom for the rest of your life. But if the set consists of X and Y, then in this case you are doomed to go to the men's room for the rest of your days. At the same time, you need to know that the man bears full responsibility for gender, since the Y chromosome is contained only in the sperm, and it is absent in the egg. So the birth of boys or girls is entirely dependent on male genetic material.

A remarkable fact is that to recreate the male sex, the Y chromosome is not needed at all. Only an initial push is needed for the development program of the male body to start. And it is provided by a special sex determination gene.

X and Y chromosomes are not equal. The first one takes on the main work. And the second only protects the genes associated with it. There are only 100 of them, while the X chromosome carries 1,500 genes.

From each X chromosome, one gene is needed to form the male sex. And to form the female sex, two genes are needed. It's like a pie recipe with one cup of flour. If you take two glasses, then everything will change dramatically.

However, you should know that the female embryo, having two X chromosomes, ignores one of them. This behavior is called inactivation. This is done so that 2 copies of the X chromosomes do not produce twice as many genes as required. This phenomenon is referred to as gene dosage compensation. An inactivated X chromosome will be inactive in all subsequent cells resulting from division.

This shows that the cells of a female embryo form a rather complex mosaic, assembled from inactive and active paternal and maternal X chromosomes. As for the male embryo, no inactivation of the X chromosome occurs in it. This means that women are genetically more complex than men. This is a rather loud and bold statement, but a fact is a fact.

But as for the genes of the X chromosome, of which there are 1500, many of them are associated with brain activity and determine human thinking. We all know that the chromosome sequence of the human genome was determined in 2005. It was also found that high percentage X chromosome genes ensure the generation of a protein that is involved in the formation of the medulla.

Some of the genes are involved in the formation of brain mental activity. These are verbal skills social behavior, intellectual abilities. Therefore, today scientists consider the X chromosome to be one of the main points of knowledge.

Every man has a so-called “Y chromosome” in his body, which makes a man a man. Typically, chromosomes in the nucleus of any cell are arranged in pairs. So for the Y chromosome there is a corresponding pair - the X chromosome. At conception the future new organism inherits all of its genetic information from its parents (half the chromosomes from one parent, half from the other). He can only inherit the X chromosome from his mother. From the father - either X or Y. If two X chromosomes are collected in the fetus, a girl will be born. If X and Y together are a boy (there cannot be two Y chromosomes in one organism). For many years geneticists believed that no other useful function nature does not assign it to the Y chromosome. However, they were wrong.

By winter, geneticists hope to completely decipher the genetic code embedded in the Y chromosome. Decoding the Y chromosome is part of the project to decipher the human genome, which is being carried out international group geneticists. Information about the genetic map of this chromosome is extremely important, since it is there that the answers to questions about the causes lie. male infertility. However, during the course of the study, it has already become clear that the Y chromosome is far from being as simple as it seemed at first.

For almost a hundred years, geneticists believed that the tiny chromosome (and the Y chromosome is indeed the smallest in the human body, noticeably smaller than its pair, the X chromosome) was simply a “stub”. The first guesses that the chromosome set of men differs from that of women were put forward in the 1920s. The Y chromosome was the first chromosome discovered using a microscope. But it turned out to be impossible to match the Y chromosome with any hereditary genetic information; for the X chromosome, the research technologies of those times (studying several generations of families to identify hereditary traits) fit quite well.

In the mid-20th century, geneticists suspected several very specific genes that might be contained on the Y chromosome. However, in 1957, at a meeting of the American Society of Human Genetics, all these theories were destroyed. The Y chromosome was officially recognized as a “dummy”, not carrying any important hereditary information. The point of view has become established that “yes, the Y chromosome carries some kind of gene that determines the sex of a person, but no other functions are assigned to it.”

And only now geneticists have begun to understand that the Y chromosome is something unique in the world of genes. It is extremely highly specialized: all the genes contained in it (and there were about two dozen of them) are either responsible for the production of sperm by the male body, or are responsible for “related” processes. And, naturally, the most important gene on this chromosome is SRY, the same gene in the presence of which the human embryo develops along the male path

The subject of genetic research is the phenomena of heredity and variability. American scientist T-X. 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 a certain amount chromosomes. It is called a karyotype. Various biological species the presence of structural units of heredity is strictly specific, for example, the human karyotype is 46 chromosomes, chimpanzees have 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. Other hereditary disease associated with sex chromosomes - 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. Male chromosomes humans and mammals are part of 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 a 23rd pair, so the karyotype of a man can be represented as 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 sea 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 are large, with a huge margin 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 the development ( anatomical structure external and internal genital organs), as well as on 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, body hair growth female type, regulate menstrual cycle and the course of pregnancy.

Some vertebrates, fish, and amphibians have biological active substances, produced by the gonads, strongly influence the development of primary and secondary sexual characteristics, and 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. Male gender and all corresponding anatomical and physiological signs 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 female glands- Müllerian duct and male gonads - Wolffian canal) 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 disorders this gene in the embryo leads to the development 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.

Main diagnostic signs is pathological growth of the mammary glands, osteoporosis, 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.

Y-chromosome

In the body of every man there is a so-called Y-chromosome that makes a man a man. Typically, chromosomes in the nucleus of any cell are arranged in pairs. For Y- paired chromosome is X-chromosome. At conception, the future new organism inherits all of its genetic information from its parents (half the chromosomes from one parent, half from the other). From his mother he can only inherit X- chromosome, from the father - either X, or Y. If an egg contains two X- chromosomes, a girl will be born, and if X- And Y- chromosomes - boy.

For almost 100 years, geneticists believed that the tiny chromosome (a Y-the chromosome is really the smallest, noticeably smaller X-chromosome) is simply a “stub”. The first guesses that the chromosome set of men differs from that of women were put forward in the 1920s. Y-chromosome was the first chromosome discovered using a microscope. But to determine the presence of any genes localized in Y- chromosome turned out to be impossible.

In the middle of the 20th century. geneticists have suggested that several very specific genes may be contained in Y- chromosome. However, in 1957, at a meeting of the American Society of Human Genetics, these hypotheses were criticized. Y-chromosome was officially recognized as a “dummy”, not carrying any important hereditary information. The point of view has been established that “ Y“The chromosome, of course, carries some kind of gene that determines the sex of a person, but no other functions are assigned to it.”

Just 15 years ago Y- the chromosome did not arouse much interest among scientists. Now decryption Y- chromosomes is part of a project to decipher the human genome, which is carried out by an international group of geneticists. During the study it became clear that Y-the chromosome is far from being as simple as it seemed at first. Information about the genetic map of this chromosome is extremely important because It is here that the answers to questions about the causes of male infertility lie.

Research Y- chromosomes may provide answers to many other questions: Where did man appear? How did the language develop? What makes us different from monkeys? Is the “war of the sexes” really programmed into our genes?

Now geneticists have begun to understand that Y-chromosome is something unique in the world of chromosomes. It is extremely highly specialized: all the genes contained in it (and there were about two dozen of them) are responsible either for the production of sperm by the male body, or for “related” processes. And, naturally, the most important gene on this chromosome is SRY– in the presence of which the human embryo develops along the male path.

Approximately 300 million years ago, it did not exist in nature Y- chromosomes. Most animals had a pair X- chromosomes, and sex was determined by other factors such as temperature (in some reptiles such as crocodiles and turtles, the same egg can still hatch into either a male or a female, depending on temperature). Then a mutation occurred in the body of a certain mammal, and the new gene that appeared began to determine “ male type development" for carriers of this gene.

The gene survived natural selection, but to do this it needed to block the process of replacement with an allelic gene from X-chromosomes. These long-standing events determined the uniqueness Y- chromosomes: it is found only in male organisms. Investigating mutations in Y- chromosome, scientists can estimate how distant (in a genetic sense) men from two ethnic groups are from our common ancestor. Some of the results obtained in this way were quite surprising.

Last November, a branch of biology called archaeogenetics took a big step forward. Leading scientific journal, Nature Genetics, suggested new version family tree humanity, based on hitherto unknown variations, so-called haplotypes Y- chromosomes. These data confirmed that the ancestors modern people migrated from Africa.

It turned out that “genetic Eve,” the progenitor of all humanity, is 84 thousand years older than “genetic Adam,” if age is measured by Y- chromosome. Female equivalent Y- chromosomes, i.e. The genetic information passed only from mother to daughter is known as m-DNA. This is the DNA of mitochondria, which is the source of energy in the cell.
For the past few years, it has been generally accepted that "mitochondrial Eve" lived about 143 thousand years ago, which does not fit with the estimated age of "Adam" of 59 thousand years.

In fact, there is no contradiction here. These data only suggest that the different chromosomes found in human genome, appeared in different times. About 143 thousand years ago, a new variety of m-DNA appeared in the gene pool of our ancestors. It, like any successful mutation, spread more and more widely until it crowded out all other varieties from the gene pool. This is why all women now carry this new, improved version of m-DNA. The same happened with Y- chromosome in men, but it took evolution another 84 thousand years to create a version that could displace all competitors.

It is not yet clear what the success of these new versions was based on: perhaps an increase in the reproductive ability of the offspring of their carriers.

Research Y-chromosomes not only allow us to trace migrations ancient peoples, but they can also tell what part of the genome a man shares with another bearer of the same surname (since both the man’s surname and his Y-chromosomes are inherited through the male line). This technique can also be used to determine the alleged name of the criminal based on traces of his DNA at the crime scene.

Data obtained during the study Y-chromosomes confirm that the “war of the sexes” is programmed in genes. The fact that men and women have different life programs is now common knowledge. While a man can theoretically have an almost unlimited number of natural children, women are limited in this.

Special position Y- chromosome allows the genes located on it to influence only the male individual and “not worry” about how they affect female individuals.

It was found that the genes responsible for the production of sperm proteins mutate very quickly, apparently due to intense competition. Y-chromosome contains large number these genes, and researchers are now trying to understand which ones are involved in this competition.

Availability Y- chromosome is a risk factor for the fetus due to the maternal immune response. This may explain some interesting patterns. For example, according to statistics, the more older brothers a man has (namely, brothers, not sisters), the more likely he is to develop homosexual tendencies. One possible explanation for this fact is that in Y- There is a gene on the chromosome responsible for the production of a masculinizing hormone called AMH. This hormone stops the development of glands, which, in its absence, turn into the uterus and ovaries. In addition, AMN causes immune reaction from the mother’s body, and the antibodies produced in this case prevent the hormone from performing another important function, namely, to direct the development of the fetal brain according to the male type.

Isolation is one of the most important features Y- chromosomes. Copying genes is accompanied by errors. When eggs and sperm are formed, parts of the paired chromosomes are swapped, and the damaged areas are discarded. But Y-the chromosome has closed its borders, and this creates “abandoned lands” where repair and renewal of genes does not occur. Therefore, gene structures gradually decline, and once functional genes become useless.

The common picture of DNA copying as something like photocopying fails to convey the true dynamism of the genome. Although nature has tried to ensure the maximum accuracy of this procedure, just one piece of DNA, like an asteroid invading someone else's chromosome, can instantly change the sequence carefully preserved for many thousands of generations. These uninvited guests are called jumping genes, or transposons.

The vast majority of genes never leave their original chromosome. In contrast, jumping genes are “genome wanderers.” Sometimes they “jump” from one chromosome and “land” in a random place on another. They can insert themselves into the middle of a gene, causing chaos, or they can “moor” at the edge, slightly modifying its function. Aliens are usually “expelled” from ordinary chromosomes due to endless mixing of genes, but once on Y-chromosome they remain in it for millions of years. Sometimes, quite by accident, it allows them to do something wonderful. "Jumping emigrants" could turn Y-chromosome into the start button that starts evolution. The first of these Y- there were immigrants DAZ, discovered by D. Page (USA).

At the time when D. Page began to study Y-chromosome, all that was known about it was that it contained a gene SRY, which in right moment triggers the development of male organs in the embryo. It is now known that Y-chromosome contains more than twenty genes (compare with 2 thousand genes in X-chromosome). Most of these genes are involved in sperm production or help the cell synthesize proteins. Gene DAZ probably arrived in Y- chromosome about 20 or 40 million years ago, around the time when the first primates appeared (perhaps the reason for their appearance was DAZ). The absence of this gene in a man’s body leads to a decrease or complete absence spermatogenesis. According to statistics, one in six couples have problems conceiving a child, and for 20% of them the key factor is male sperm.

Currently, ectopic fertilization technology partially solves this problem. But bypassing the laws of nature is not in vain. Infertility, as paradoxical as it may sound, becomes hereditary.

Recently, British researchers made a bold assumption: the critical factor in the emergence of speech in humans was precisely a certain “jumping gene” that invaded Y-chromosome.

Gene DAZ by enhancing spermatogenesis allowed primates to flourish, but what gene was the impetus for the separation of humans from the primate lineage? A direct way to find it is in the human and chimpanzee genomes. A more elegant way is to imagine what the consequences of such mutations would be and where these mutations might be found.

This is exactly what was done at Oxford. At first, researchers assumed that there was a certain gene that had such an influence on brain development that speech became possible. Moreover, it was suggested that this gene takes a different form in men and women.

At a conference in London in 1999, another research group announced that Y-gene detected on chromosome PCDH, whose activity most likely affects the functioning of the human brain, but not primates. This makes it a good candidate for a speech gene. Primates have it X-version ( PCDHX), but at some point in evolution it jumped to Y- chromosome.

Scientists have been able to trace the connection Y-versions of this gene ( PCDHY) with two turning points in human evolution. The first of these occurred about 3 million years ago, when the size increased human brain and the first tools appeared. But that's not all. A piece of DNA carrying PCDHY, transformed again, splitting into two parts, so that the resulting segments turned over in their places. According to scientists, this happened 120–200 thousand years ago, i.e. just at the time when it happened big changes in the manufacture of tools.

Human African ancestors developed the ability to transmit information using symbols. Circumstantial evidence is all well and good, but how does this gene actually function? On at the moment there are more questions than answers here, but the available data do not contradict the theory about the connection of this gene with the appearance of speech. It is likely one of a family of genes known as cadhedrins. They synthesize proteins that make up the membrane of nerve cells and are thus involved in the transmission of information. Genes PCDHX/Y active in some areas of the human fetal brain.

But behind all these discoveries lies one big mystery. Y- the chromosome can be thought of as a model of a capitalist economy. The winners, the genes that give an advantage, take everything because they don't mix with genes from other chromosomes. Outsiders, because they usually affect fertility, going bankrupt almost instantly. That is, the genes that survive here must do something truly valuable for the organism.

More likely, Y-chromosome has lost most of its genes during evolution, but all the remaining genes thrive. They must perform some elusive function, incomprehensible to us. Probably, to clarify this function, it is necessary to investigate the connection genetic markers, allowing you to trace a person’s ancestry with his abilities. The idea is dangerous in terms of ethical correctness, but it will provide an opportunity Y- chromosome will surprise us more than once.

The male Y chromosome is not a dead end of evolution, but is changing very actively. Such conclusions were made by geneticists when comparing the set of genes in the chromosome of humans and chimpanzees, which survived 6 million years of separate evolution. The unexpected genetic diversity is explained by the peculiarities of the functioning of genes involved in the formation of germ cells.

In most mammals, sex is determined by them: the male body is the carrier of the X- and Y-chromosomes, and women “make do” with two X-chromosomes. Once this division did not exist, but as a result of evolution about 300 million years ago, chromosomes differentiated. There are variations whereby some men's cells contain two X chromosomes and one Y chromosome, or one X chromosome and two Y chromosomes; Some women's cells contain three or one X chromosome. Occasionally, female XY organisms or male XX organisms are observed, but the vast majority of people still have a standard configuration of sex chromosomes. For example, the phenomenon of hemophilia is associated with this feature. The defective gene that impairs blood clotting is linked to the X chromosome and is recessive. For this reason, women only endure the disease without suffering from it themselves due to the presence of a duplicate gene due to the second X chromosome, but men in a similar situation carry only a defective gene and get sick.

One way or another, the Y chromosome has traditionally been considered weak point male organisms, reducing genetic diversity and hindering evolution. However latest research showed that fears about the extinction of the male race are greatly exaggerated: the Y chromosome does not even think of stagnating. On the contrary, its evolution is very active, it changes much faster than other areas genetic code person.

A study published in Nature (Jennifer F. Hughes et al., Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content) showed that a specific part of the Y chromosome of humans and one of its closest relatives, chimpanzees, is very different . Over the 6 million years of separate evolution of monkeys and humans, the fragment of the chromosome responsible for the production of germ cells has changed by a third or even half. The rest of the chromosome is actually quite constant.

Human evolution. Source "Eternal Youth"

Scientists' assumptions about the conservatism of the Y chromosome were based on objective factors: being transmitted from father to son without changes (for the X chromosome there are as many as three options - two from the mother and one from the father, all of them can exchange genes), it cannot gain genetic diversity from the outside, changing only due to the loss of genes. According to this theory, in 125 thousand years the Y chromosome will finally die out, which could be the end of all humanity.

However, for 6 million years of separate evolution of humans and chimpanzees, the Y chromosome has been successfully changing and progressing. IN new job, conducted at the Massachusetts Institute of Technology, talks about the Y chromosome of chimpanzees. The human Y chromosome was deciphered in 2003 by the same group led by Professor David Page.

The results of the new study surprised geneticists: they expected that the gene sequence on the two chromosomes would be very similar. For comparison: in the total DNA of humans and chimpanzees, only 2% of genes are different, and the Y chromosome differs by more than 30%!

Professor Page compared the process of evolution of the male chromosome to a change in the appearance of a house, the owners of which remain the same. “Despite the fact that the same people live in the house, almost constantly one of the rooms is completely updated and renovated. As a result, after a certain period of time, as a result of “room-by-room” renovation, the entire house changes. However, this trend is not normal for the entire genome,” he noted.

The reason for this unexpected instability of the Y chromosome is not yet precisely clear. Scientists suggest that genetic diversity in it is ensured by instability to mutations. The usual mechanism for “repairing” genes fails on the Y chromosome, opening the way for new mutations. Statistically, a larger number of them become fixed and change the genome.

In addition, these mutations are subject to significantly greater selection pressure. This is determined by their function - the production of germ cells. Any beneficial mutations are more likely to be fixed, since they act directly - increasing the ability of an individual to reproduce. At the same time, ordinary mutations have an indirect effect - increasing the body's resistance to disease or harsh conditions environment, For example. Thus, the benefit of a mutation in a nonspecific DNA section will only be revealed if the organism falls into the corresponding unfavorable conditions. In other cases, mutant and non-mutant organisms will perform similarly. Fertility appears very quickly - already in the second generation. An individual either reproduces as a result of mutation more successfully and leaves numerous offspring, or reproduces noticeably worse and cannot increase the share of its genes in the general population. This mechanism functions more efficiently in chimpanzees, whose females constantly mate with a large number males. As a result, the germ cells enter into direct competition, and “selection” occurs as efficiently as possible. In humans, due to more conservative models of reproduction, the Y chromosome has not evolved so rapidly, geneticists say. This hypothesis is supported by the fact that the parts of the chromosome involved in sperm production are most different between humans and chimpanzees.