THE MALE sex-determining chromosome is on the way out, according to a genetics expert who will talk on the issue in Dublin tomorrow.
But there’s a while yet to say goodbye because it is unlikely to disappear completely for another six million years or so.
The Y chromosome has evolved to be strange, says Prof Jenny Graves from the Australian National University in Canberra, who explains that females have two copies of the X chromosome while males instead have one X and a Y, which carries the SRY gene for testis function.
“The Y chromosome is quite a large chunk of DNA but it is full of junk and there are only 45 genes on it. That’s hardly any compared to the X chromosome, which has about 1,345 genes on it,” she said.
By looking at the genomes of Australian fauna, including kangaroos and platypuses, Graves’s lab has worked out that the Y chromosome has been losing about 7.8 genes every million years. “We know the Y chromosome had about 1,345 genes on it 166 million years ago – it would have been identical to the X – and we know that all but 45 of those have gone,” she explained.
“At that rate, the last 45 genes are going to disappear in about 5.8 million years.”
Prof Graves noted that other animals had already seen even greater reductions – Eastern European mole voles appear to have lost their Y chromosomes and SRY genes about 20 million years ago, which led to new species evolving.
“They have babies and you wouldn’t even know they had a different sex-determining system unless you looked,” she said. “So the future isn’t quite as bleak as you might think. If we come back in 5.8 million years, we could find no humans or maybe two human species.”
Prof Jenny Graves will talk on The Decline and Fall of the Y chromosome and the Future of Men tomorrow at 7pm at the Royal College of Surgeons in Ireland, 123 St Stephen’s Green, Dublin 2. See www.rcsi.ie. To reserve a place at this Annual Outreach Lecture, call 01-402 2373 or e-mail outreach@rcsi.ie
