The Y chromosome is disappearing – What does this mean for men?
A new gene may be the future
The sex of embryos in humans and other mammals is determined by the Y chromosome. Two X chromosomes define female, and one X along with a smaller Y define male. Note, of course, that the names have nothing to do with their shape. The X contains about 900 genes that define sex-independent functions. But the Y contains only 55 genes and simple repetitive DNA that doesn’t seem to do anything. However, it contains an important gene that initiates male development in the embryo.
About 12 weeks after conception, this gene turns on other growth-defining factors, male hormones such as testosterone and its derivatives, ensuring that the embryo will develop as a boy. This SRY gene was discovered in 1990 and works by activating a genetic pathway that starts with the SOX9 gene, which is key to male identification in all vertebrates, even though it is not on the sex chromosomes.
But the Y chromosome is gradually degenerating and may disappear in a few million years, leading to the end of humanity unless we develop another sex gene. The good news is that we already have two species of rodents that have lost the Y chromosome and survived.
Eastern European moles and Japanese rats have some species that have completely lost the Y chromosome, with the X chromosome remaining in single or double doses in both sexes. For the Japanese rat it was discovered that the Y had moved to other chromosomes. A small difference in the sex gene SOX9 on chromosome 3 – a small duplication of just 17,000 base pairs out of 3 billion – was present only in male rats.
What does this mean for the future of men?
Some lizards and snakes consist only of females and can lay eggs from their own genes, also known as parthenogenesis. This cannot happen in humans and other mammals, as we have at least 30 critical genes that only work if they come from the father. So will the disappearance of Y spell the end of humanity?
The new findings support a different version – that humans will evolve a different sex-determining gene. However, the evolution of a sex gene carries risks. What if a new system evolves in different parts of the world? A “war” of sex genes can lead to new species, as happened with the two rodents we mentioned. Thus, if one were to visit Earth in 11 million years, one might find multiple species of humans distinct from the different systems of gender separation…
The research was published in the Proceedings of the National Academy of Science .
