“The human Y is in the very last stages of degeneration, and the big question is how long till it, too, gets lost, and what will happen when it does. If it goes on degenerating at the same rate it has over the last 150 million years, it has only a few million years to go,” [sex chromosome geneticist Jenny] Graves said.
The Y chromosome itself therefore doesn’t flick the developmental switch that makes an animal grow male traits, rather the SRY gene on the chromosome starts the chain of events. All animals begin development as females: the SRY gene “turns on” other genes that lead to a fetus developing as male, including the SOX9 gene that triggers the development of testes.
In humans, the SRY gene is on the Y chromosome, so if the Y eventually disappears, will we have no more males? The PNAS paper, which investigates how the male spiny rat stuck around, shows us why males probably aren’t going anywhere.
Share this article
The researchers found that the male spiny rats had a duplicated region on their chromosome three, right next to the SOX9 gene itself. They also found that this duplication boosts the activity of SOX9 and thus effectively replaces SRY. Therefore, the spiny rats have evolved a way to make males using a completely different chromosome. The team estimates that this duplication evolved around 2 million years ago.
