24 February 2012

Rumors about the extinction of men turned out to be greatly exaggerated

Y-chromosome – be!

Text: Kirill Stasevich, CompulentaThe rate of disappearance of the Y chromosome is greatly exaggerated – the male sex chromosome of primates has lost only one gene over the past 25 million years.

The history of the Y chromosome began 200-300 million years ago; it is believed that it first appeared in the common ancestor of all mammals. Of course, living organisms were divided by sex before that, but earlier such a division, according to scientists, was due to environmental factors. Now, gender has received a strict genetic definition. The SRY partner gene broke away from the SOX3 gene. The chromosome that received the SRY gene became male, the chromosome with the SOX3 gene became female.

Human X- and Y-chromosomes under an electron scanning microscope (photo by Biophoto Associate)

Like all ordinary paired chromosomes, X and Y initially exchanged similar sites during recombination. But gradually the male chromosome lost fragments of DNA, and she had fewer and fewer genes suitable for exchange with the X chromosome. Now our sex chromosomes can only exchange material from small end sections. In 2002, an article appeared in the journal Nature in which a group of Australian scientists predicted the imminent death of the male chromosome – within about 10 million years (not such a long time on an evolutionary scale). It should be clarified that this does not necessarily mean the disappearance of the male sex itself: in some mammals (for example, blind and bristly rats), with the missing Y chromosome, the sex genes are distributed on other chromosomes.

The death of the Y chromosome was vigorously discussed by the scientific community until a group of geneticists from the Whitehead Institute (USA) compared the sex chromosomes of humans, chimpanzees and rhesus monkeys. Chimpanzees separated from a common ancestor with humans about 6 million years ago, and during this time their Y chromosome has lost a large number of different genes. But one group of genes not only remained, but also multiplied due to copies. These are the genes responsible for sperm production. This specialization of the sex chromosome, according to scientists, is important for those species whose males practice promiscuous sexual relations. In this case, only one thing is required from the Y chromosome - as many sperm as possible, and whether it knows how to do something else is completely unimportant.

To more closely trace the history of the male chromosome in primates, the researchers tested the sequence of the Y chromosome in rhesus monkeys. These monkeys followed their evolutionary path even earlier than chimpanzees – 25 million years ago. Scientists compared the chromosomes of macaques and humans. It should be noted here that for all the difference, the Y chromosomes of the two species encode mostly the same genes. The researchers expected that macaques, due to a longer period of independent evolution, would have even more copies of "sperm" genes and fewer general-purpose genes. But then scientists made an unusual discovery: it turned out that the difference between the Y chromosomes of humans and rhesus monkeys lies in one gene. That is, for 25 million years of our separate evolution with macaques, the human Y chromosome has lost a single gene.

Scientists publish the results of their research in the journal Nature (Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes).

Once upon a time, the male sex chromosome may have been rapidly losing genes, but by the time primates appeared on Earth, the rate of its disappearance had greatly slowed down. In general, according to scientists, we can safely count on the fact that in 50 million years human men will have their Y chromosome. Unless, of course, our species itself disappears by virtue of its own activity. In this regard, the authors of the work somewhat maliciously suggest that their colleagues pay attention to more pressing problems like global warming, and not worry about the fate of the Y chromosome.

Prepared by the Whitehead Institute: Theory of the "rotting" Y chromosome deal a fatal blowPortal "Eternal youth" http://vechnayamolodost.ru


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