Australia was a rather late entry into the big genome business, but genomes of our unique animals are proving a goldmine of information. This is because Australia has been cut off from other continents for a long time, so the genes and regulatory systems of our animals have had time to evolve differently. From the mid-2000s, when Australia quit the race to sequence the first marsupial, several of our animals were sequenced overseas, including the kangaroo and platypus. Now sequencing has become so cheap and available, the world is clamouring for more – many Australian marsupials, monotremes, birds, snakes and lizards are on the list.
These genome differences can provide insights for all sorts of studies, including basic investigations of animal development that can be used to improve medical practice. Our studies have been on sex, and here, Australian animals – kangaroos, platypus and dragon lizards, have delivered stunning insights into what chromosomes and genes determine sex, how they work and how they evolved.
In humans and other mammals, females have two X chromosomes, but males have a single X, and a Y that bears a gene (SRY) that induces testis differentiation in the embryo and switches on hormones that masculinize it. The human X has more than 1500 genes, but the tiny Y is a genetic wasteland – full of genetic junk and bearing only 45 genes, most active only in testis. To discover how human sex chromosomes got to be so weird, we compare the chromosomes, genes and DNA in distantly related mammals and even birds and reptiles (with completely different sex determining systems). Kangaroo sex chromosomes reveal the original mammal sex chromosomes, while the bizarre platypus sex chromosomes (more related to those of birds) tell us that human sex chromosomes and the SRY gene are relatively young. The human X and Y evolved from an ordinary chromosome pair as the Y degraded progressively. The Y is predicted to disappear in just 5 million years. If humans don’t become extinct, new sex determining genes and chromosomes will evolve, maybe leading to the evolution of new hominid species.