Translated material
Where is the masculine gender going?
Many "experts" say: "the male Y-chromosome - and with it the entire male gender - are in danger of extinction" ...
Epigraph- Tell me, professor! You said that in 5 million years the Sun will reach such a size that it will swallow the Earth. This is true? - No. This will happen only after 5 billion years. - A! Well, thank God! Today in the press...
Epigraph- Tell me, professor! You said that in 5 million years the Sun will reach such a size that it will swallow the Earth. This is true? - No. This will happen only after 5 billion years. - A! Well, thank God!
Today, news is circulating in the press that soon “the world will be left without men”, that “the male Y-chromosome - and with it the entire male race - are under the threat of extinction”, that “men will disappear like dinosaurs”, “will disappear with face of the Earth”, “disappear as a biological species”. Can these sensations be trusted? What is the Y chromosome and what is it for? What is really happening to her? Is there really a threat to the male population? About this - this article.
Human hereditary material is organized into 22 pairs of non-sex chromosomes (autosomes) and two sex chromosomes. Half of our chromosomes come from our father and half from our mother. Women have two X chromosomes, while men have one X and one Y chromosome. In fact, the picture is somewhat more complex. Approximately one in five hundred men has two X and one Y chromosome (XXY), and one in 1000 has one X and two Y (XYY). Every thousandth woman has three X (XXX).
Having more than two sex chromosomes is not fatal, but it can lead to developmental disorders. In XYY-men, violations are slightly expressed: there are slight deterioration in mental development, increased growth, but at the same time fertility (the ability to leave offspring) is preserved. XXY men tend to be infertile, have less of the male sex hormone testosterone, and less developed genitals. XXX women tend to be fertile, in some cases developmentally delayed. A change in the number of copies of autosomes is much more dangerous: three copies of the 21st chromosome are the cause of the development of Down syndrome, tripling of any of the other chromosomes is incompatible with life.
It turns out that the sex of people is determined by the presence or absence of the Y chromosome: if there is a Y chromosome, a man is obtained, if it is not, a woman. Such a sex determination system is not the only one possible in the animal world. For example, in the fruit fly Drosophila, sex is determined by the number of X chromosomes and does not depend on the presence of a Y chromosome. In birds, unlike humans, two identical sex chromosomes are observed in males, while females have different sex chromosomes. The platypus (a unique egg-laying mammal with a beak) has as many as 10 sex chromosomes, which are linked in chains of five: there are XXXXXXXXXXX-females and XYXYXYXYXY-males. Moreover, one part of the platypus sex chromosome chain is similar to the sex chromosomes of birds, and the other part is similar to the sex chromosomes of other mammals.
In very rare cases, among humans, rodents and some other mammalian species, one can meet a male without a Y chromosome, as well as a female with a Y chromosome. It was shown that not the entire Y chromosome is necessary for sex determination, but only a small part of it, just one gene. The SRY gene, located on the Y chromosome, is responsible for the development of the testes. If this gene "jumps" to another chromosome, then an XX male can be obtained. If, as a result of a mutation, the SRY gene is disabled on the Y chromosome, an XY female can be obtained.
In 1991, the scientific journal Nature published the work of molecular biologist Peter Koopman, who succeeded in inserting the SRY gene from the mouse Y chromosome into mouse embryos with two X chromosomes. Such transgenic mice appeared to be male in appearance. So it was confirmed that the key genetic difference between a man and a woman lies in a single gene.
But how can a single gene have such a profound effect on a person's development? It turned out that the SRY gene can activate other genes responsible for the development of male sexual characteristics. In the female, these genes are turned off, but the appearance of the SRY gene can turn them on. In other words, every woman's genome contains almost all the necessary instructions for the development of a man, but these instructions are kept under lock and key. The SRY gene is the key to this lock.
Although Koopman's work showed that one gene was enough to produce XX mice with all the external features of males, the resulting males were infertile. This means that for the full development of the male, one gene is still not enough. Nevertheless, many scientists are inclined to believe that the number of genes important for the development of full-fledged men is small on the Y chromosome.
Recent evidence suggests that the Y chromosome became the sex chromosome approximately 150 million years ago. Then the X and Y chromosomes were very similar, as well as modern non-sex chromosomes. Since then, the Y chromosome has steadily decreased in size and has lost about 97% of its genes. Having become a sex chromosome, she began to accumulate genes that are useful for men, but harmful for women, and gradually get rid of everything else.
In addition, the Y chromosome mutates almost 5 times faster than the rest of the chromosomes. It is believed that this is due to the fact that the appearance of male germ cells is preceded by a large number of divisions. The fact is that with each cell division, it is necessary to copy the chromosomes so that each new cell gets a complete set of genetic material. But the DNA copying system is not perfect: with each copying, errors, peculiar typos, and mutations occur. The Y chromosome goes through a large number of copies in each generation, because it is inherited only through male germ cells, which means it accumulates more errors associated with copying. Autosomes* are inherited from both men and women, which means that in half of the generations they are inherited through female germ cells. As a result, they go through fewer divisions per generation on average and accumulate fewer mutations.
If we roughly calculate the rate of disappearance of genes from the Y chromosome and the number of genes remaining on it, we can imagine that the Y chromosome will lose all its genes in about ten million years. Today there is a discussion about whether the Y-chromosome is threatened with complete extinction in the future. First, Koopman's experiments show that the Y chromosome is not so necessary: if a couple of genes important for determining sex jump from the Y chromosome to the autosome, we will get a new sex determination system. In such a system, the Y-chromosome can be eliminated without any special consequences. Indeed, in some rodent species, the Y chromosome was completely lost during evolution, which indicates that the scenario described above is indeed possible. Another point of view says that nothing will happen to the Y chromosome. Today, it has been shown that there are a number of evolutionary mechanisms that actively preserve the genes remaining on the Y chromosome. It is not necessarily true that the Y chromosome will continue to lose the genes that remain on it at the same rate as it lost them before. Despite the existence of different points of view, scientists agree that a decrease in Y will not lead to catastrophic consequences for humanity. The men will stay.
* All chromosomes in the cells of dioecious animals, plants and fungi, with the exception of sex chromosomes.