Exploring weird Australian genomes

Then later on while the young is still in the pouch and still suckling, it receives a completely different constitution of milk. The extraordinary thing is that the two completely different constitutions of milk are delivered by two teats lying next to each other. We want to know what’s in that milk, particularly the growth factors, and how the kangaroo switches from one type of milk to the other - how do the two bowsers deliver different milks?

Researchers have been studying kangaroo milk and saliva for some time because the pouch is a very dirty, grotty sort of place for a poor little pouch young who doesn’t even have an immune system. Something must be killing off the bacteria. As reported in The Age recently, kangaroo milk contains a very powerful new antibiotic. There may be a number of antibiotics in milk that can be harnessed for treating bacterial infections in humans. Kangaroo milk may be a strange place to look for new products but it looks like it has delivered.

My own interest is in genome evolution and I’m particularly interested in the evolution of the sex chromosomes. We can find out a lot about where and how the sex chromosomes originated by comparing sex chromosomes from humans, kangaroos and even platypus.

In humans, as in other mammals, females have two copies of a large gene rich X chromosome (approximately 1,000 genes), while males only have one copy of the x plus a small Y chromosome. The Y chromosome is a very peculiar little chromosome with only 45 genes. It seems to be specialised for a male role, with genes for sex determination and making sperm. The Y has always been known to be very peculiar so there is been a lot of interest in it.

There are two models for the Y chromosome. The model we were all brought up with was the Y as a macho little thing because if you have a Y you’re male and that’s it. But it turns out that’s only because the Y chromosome has the SRY gene on it. The other theory is that the Y is a selfish sort of entity and it grabs genes from other parts of the genome that are handy in males. But our work on comparative mapping says that the Y is merely a wimp, a relic of the X chromosome. It started off being identical to the X but over millions of years it has been losing genes and there are hardly any left.

This, of course, makes men very anxious. Will the Y chromosome disappear? I have predicted that at the rate it’s going the Y chromosome will disappear in something like 15 million years. This doesn’t necessarily mean that males will disappear. It’s possible that we’ll evolve a new sex determining gene somewhere else in the genome.

The other interesting thing about this hypothesis that the Y chromosome is a relic of the X, is that the genes on the Y are all, or mostly, evolved from genes on the X. We’ve done a lot of work on some of the special function genes, like the sex determining gene SRY, and other genes like RBMY which is critical for spermatogenesis, and we found they all evolved from genes on the X and, oddly enough, appear to be involved in brain development and function. So it looks like intelligence genes that find themselves on the Y chromosome have been commandeered to make them into fertility genes.

Will the possession of sex and spermatogenesis genes save the Y? Probably not. We know that some genes needed for making sperm in mice have been lost from the primate Y. If this gene can be lost in other species, why not the SRY gene itself? If it becomes inactive and then gets lost there is no reason to keep a Y chromosome at all - it can just disappear

So I hope I have answered the question of why sequence genomes of Australian mammals (are important). Animal genomes can give depth and meaning to the human genome sequence: our Australian animals, are particularly good for finding new genes and the sequences that control them; they help us understand diseases and possibly lead to new treatments and even cures; they can lead to the development of new antibiotics, new drugs and better breeds of animals; and they also help us discover where our genome came from and how it has changed.

In fact, comparative genomics is giving us information that can help us discover how humans are made and how humans function. It’s been called the greatest scientific adventure of our age. The prestigious journal Science thinks so too - naming evolutionary genomics the “breakthrough of the year” at the end of 2005.