Platypus genome unravelled
8 May 2008
The duck-like bill, webbed feet and venomous leg spur of the male platypus make it an unusual mammal. Consider that the females lay eggs, suckle young through skin rather than nipples and hunt underwater in a thick fur coat and the creature becomes even more intriguing. Now, the genes behind this combination of reptilian, bird and mammal-like characteristics have been uncovered.
An international collaboration of scientists sequenced the platypus genome using DNA from a female nicknamed Glennie that lives in Glenrock Station, New South Wales. The analysis is published in Nature.
The platypus, Ornithorhynchus anatinus.
Image credit: Nicole Duplaix/Getty Images
The platypus belongs to the monotreme family of mammals. This means that it has a single hole for its reproductive and digestive systems. Its neuro-anatomy is also unusual – it uses electro-sensory system to locate prey while it forages with its eyes and nostrils closed under water.
The team searched Glennie the platypus’ genome for DNA sequences unique to monotremes as well as those known to be involved in venom production, electro-reception and milk production in other species. They then compared the platypus genome to those of other mammals (mouse, human and opossum) and a bird - the chicken.
The results show that the platypus genome is a strange blend of genes linked to mammalian, bird-like and reptilian features. Dr Ewan Birney who worked on the platypus genome analysis at the European Bioinformatics Institute in Cambridge said:
‘Tthe platypus genome is much more of a melange than anyone expected.’’
The genome analysis found that the proteins that make both reptile and platypus venom have origins in the same families of genes even though they evolved independently, that milk-producing genes are present even though the platypus lays eggs and that genes linked to the immune system have expanded to reflect the animals unusual biology.
The platypus makes its home in fast flowing streams
Image credit: WIRES Northern Rivers
It also showed that the platypus has ten sex chromosomes, in comparison humans have two. Furthermore, the gene sequences responsible for determining sex are more similar to those in birds than in mammals.
Professor Chris Ponting of the MRC Functional Genomics Unit at the University of Oxford who helped to unravel the platypus genome said:
‘‘This is our ticket back in time to when all mammals laid eggs while suckling their young on milk. The platypus genome is extremely important because it is the missing link in our understanding of how we and other mammals first evolved, it also provides an essential background to future advances in understanding mammalian biology and evolution.’’
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