The Y chromosome may be a symbol of masculinity, but it is becoming increasingly clear that it is anything but strong and enduring. Although it carries the "master switch" gene, SRY, that determines whether an embryo will develop as male (XY) or female (XX), it contains very few other genes and is the only chromosome not necessary for life.
Women, after all, manage just fine without one!
What's more, the Y chromosome has degenerated rapidly, leaving females with two perfectly normal X chromosomes, but males with an X and a shriveled Y. If the same rate of degeneration continues, the Y chromosome has just 4.6 million years left before it disappears completely. This may sound like a long time, but it is not when you consider that life has existed on Earth for 3.5 billion years.
Now, could that lead to our extinction or will we evolve a new sex gene? The good news is two branches of rodents have already lost their Y chromosome and have lived to tell the tale.
A new paper in Proceedings of the National Academy of Science shows how the spiny rat has evolved a new male-determining gene.
The imminent – evolutionarily speaking – disappearance of the human Y chromosome has elicited speculation about our future.
Some lizards and snakes are female-only species and can make eggs out of their own genes via what’s known as parthenogenesis. But this can’t happen in humans or other mammals because we have at least 30 crucial “imprinted” genes that work only if they come from the father via sperm.
To reproduce, we need sperm and we need men, meaning that the end of the Y chromosome could herald the extinction of the human race.
The new finding supports an alternative possibility – that humans can evolve a new sex-determining gene. However, the evolution of a new sex-determining gene comes with risks. What if more than one new system evolves in different parts of the world?
A “war” of the sex genes could lead to the separation of new species, which is exactly what has happened with mole voles and spiny rats. So, if someone visited Earth in 11 million years, they might find no humans – or several different human species, kept apart by their different sex determination systems.
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