I'm going to a lecture tonight by Prof Jennifer Graves of the Australian National University entitled 'The Decline and Fall of the Y Chromosome and the Future of Men'. Should be interesting. I'll update tomorrow. Here is the ad:
'The Decline and Fall of the Y Chromosome and the Future of Men'
Professor Jennifer Graves
(PhD, FAA Director, ARC Centre of Excellence for Kangaroo Genomics Head, Comparative Genomics Research Group Research School of Biological Sciences The Australian National University Canberra, ACT 2601, AUSTRALIA)
On Wednesday 20th May 2009
To celebrate Charles Darwin's 200th year anniversary, the 2009 Public Lecture Series will focus on the theme Evolution featuring renowned leader in the Australian and international cell biology, genetics and genomics communities Professor Jennifer Graves. Jenny is particularly well known for her theories of the origin and evolution of human sex chromosomes and sex determining genes, and her dire prediction that the Y chromosome will disappear! the topic of this current lecture. We are delighted and privileged to welcome Professor Jennifer A. Marshall Graves to our college.
Well it was very interesting...
She started the lecture by explaining the origin of the Y chromosome. It was originally identical to the X chromosome, but a mutation in a gene called SOX3 led to the emergence of a new gene called sex-determining region Y (SRY), which encodes a protein with the ability to promote the development of the testis, and hence controls male development. Following the emergence of this gene, other male-specific genes (e.g. controlling sperm production) emerged and were selected for in the same region. Over time, this resulted in difficulties to recombine between the X and Y chromosomes and the Y chromosome became highly susceptible to mutation, leading to the inactivation of many of it's genes. In fact, the Y chromosome has degraded and shrunk so much that of the 1300+ genes it once had, it now is mostly junk and contains a measly 45 active genes. At this point in the lecture, we had the first indication of the overall theme - if it continues to degrade and shrink, who is to say that it won't eventually disappear?
Next Prof Graves explained how they have studied the sex-determining mechanisms in other animals. In marsupials (she is Australian after all!) there are similar X and Y chromosomes to humans, suggesting that this mechanism is as old as the marsupial/placental spilt. However, when you look in the platypus, the sex-determining mechanism is more similar to the ZW system in birds (in this case the sex-determining gene promotes female development). What this tells us is that the X and Y chromosomes are a maximum of 166 million years old, as this is when the last common ancestor between humans and the platypuses is thought to have existed. So it seems that the Y chromosome has lost over 1300 genes in about 166 million years. Based on this, Prof Graves predicts that the Y chromosome only has about 6 million years left before it will disappear.
So what does that mean for the future of men?
Well......not much. Prof Graves speculated that a new sex-determining gene is likely to evolve, providing a new mechanism. This is where the talk got a bit fuzzy, and she didn't really go into much detail (she admitted as much in the Q&A), but there is one intriguing possibility that directly follows from her hypothesis...
If a new sex determining gene was to evolve, and the mechanism switched so that this gene promoted female development instead of male (as is the case in birds), this would eventually result in two populations, one with the SRY male-promoting gene and one with the new possibly female-promoting gene. What would happen if a member of each population mated? The offspring would have signals promoting both maleness and femaleness during their development. Prof Graves speculated that this could result in humans consisting of males, females and a third male-female hybrid! In fact she suggested that this scenario may have happened in the past, and that it would inevitably be a driving force for speciation.
Prof Graves is an excellent speaker and she has a proven track record in this area. Read an interview with her here. I'm not sure if I buy into all of her ideas about the future but it is certainly an interesting topic.
As an aside, she is a staunch defender of science and evolution and has had a few run-ins with the Discovery Institute; they have tried to use her research as evidence for intelligent design in the past (she mentioned this in her talk but I can't find a link). Because of this she is currently setting up a Dumb Design website (again, no link as yet), which will catalogue biological examples of bad design as evidence against an intelligent deity.