TWO centuries after a dead specimen was deemed so outlandish it had to be a fake, the bizarre genetic make-up of the platypus has been laid bare.
Wesley Warren at Washington University in St Louis, Missouri, led the team that sequenced the platypus genome. As expected, they found an amalgam of reptile and mammalian features, but some surprises, too.
It turns out the gene sequences responsible for determining sex are more like a bird鈥檚 than a mammal鈥檚. Though the gene that evolved into the human sex-determining gene is present, that is not its job. So the function in humans must have evolved after the platypus split from our common ancestor, about 166 million years ago. Yet the platypus has the same repertoire of milk protein genes as a cow or a human, so clearly milk evolved long before the ability to have live offspring (Nature, ).
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鈥淭he platypus has the same repertoire of milk protein genes as a cow or a human鈥�
The team also found that the platypus has a bigger repertoire of a particular class of vomeronasal receptors than any other animal, which suggests that their sense of smell is important while foraging under water. 鈥淚 don鈥檛 think anybody expected that,鈥� says Stewart Nicol at the University of Tasmania, Hobart.
The draft sequence should also end controversy over where the platypus sits on the evolutionary tree. Now there鈥檚 no doubt that it split off the branch that led to both placentals and marsupials.
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