Everyone learnt at school that the X and Y genes determine sex.
Women have a pair of XX chromosomes, and men XY. Simple.
But what you might not have been taught is that the Y chromosome is much smaller, carrying around 55 genes compared to roughly 900 on the X.
However, it seems the Y chromosome wasn’t always so small, and that’s where the problem lies.
It’s shrinking – and some scientists worry it could disappear altogether
One of them, Professor Jenny Graves, explained why, through the lens of the platypus.
‘In platypus, the XY pair is just an ordinary chromosome, with two equal members,’ she said, writing for The Conversation. ‘
‘This suggests the mammal X and Y were an ordinary pair of chromosomes not that long ago
‘In turn, this must mean the Y chromosome has lost 900 to 55 active genes over the 166 million years that humans and platypus have been evolving separately
That’s a loss of about five genes per million years. At this rate, the last 55 genes will be gone in 11 million years.’