Scientists have decoded the genome of the duck-billed platypus, and discovered that the genetic code is as weird as the animal itself. The findings, reported in the journal Nature, hold invaluable clues for understanding evolution.
When the first sample of a platypus arrived in England in 1799, the naturalist George Shaw at the British Museum thought it must be a hoax. The animal has the furry skin of a mammal adapted to an aquatic lifestyle yet has the beak of a bird. The females lactate yet lay eggs like a reptile, and the males produce venom similar to a reptile. Shaw eventually named the animal the 'platypus', after its flat, webbed feet.
Genetic analysis of the platypus has now revealed genetic modules that aligned with the mish-mash nature of its features. The study was led by Professor Jenny Graves at the Australian National University, and Wesley Warren and Richard Wilson at the Washington University in St Louis, and consisted of scientists from the UK, Europe, Japan and New Zealand as well as Australia and the US.
The team found that the platypus genome has 2.2 billion base pairs in the genome, about two thirds as many as humans, and 18,500 genes, about the same as humans. Comparison with human, mouse, chicken, dog and opossum genomes, which have all previously been sequenced, found that it shares 82 per cent homology (similarity) of its genes with those species.
One of the most notable findings was concerned with the sex chromosomes, of which the platypus has 10, compared with two in mammals: X and Y. They also seem closer to the Z and W sex chromosomes of birds, and have no sex determination gene like humans do. The platypus has one gene for a kind of yolk protein, although chickens have three. Venom proteins from the same gene families as those of a snake were found. Genes for proteins capable of detecting chemical signals were found, giving clues as to how its remarkable electrosensitive bill allows the platypus to guide itself underwater with its eyes and nose covered. Platypus milk protein genes have also been found to be conserved. 'It is such a wacky organism', says Richard Wilson.
The sequencing of the platypus genome is of great importance in understanding evolutionary pathways, and is 'priceless for understanding how fundamental mammalian biological processes have evolved' says Francis Collins, head of the US National Human Genome Research Institute which funded most of the work.