Platypus genome sequenced

UK-based researchers have revealed the genetic make-up of one of the world’s strangest mammals: the Australian platypus.

The platypus, a female nicknamed Glennie, was sequenced by scientists at the Genome Sequencing Centre of the US Washington University School of Medicine, as part of an international research collaboration including scientists from the UK and Australia. The analysis was published in the 8 May issue of Nature.

The researchers found that the diverse characteristics of the platypus are mirrored by a patchwork of genes resembling those from reptiles, birds and other mammals.

“The platypus genome is extremely important because it is the missing link in our understanding of how we and other mammals first evolved,” said lead researcher, Chris Ponting, from the MRC Functional Genomics Unit at the University of Oxford.

“This is our ticket back in time to when all mammals laid eggs while suckling their young on milk. It also provides an essential background to future advances in understanding mammalian biology and evolution.”

The researchers searched the genome for DNA sequences that are unique to the monotremes, as well as those known to be involved in venom production, electro-reception (the specialised system in the platypus bill that uses electricity to detect food under water) and milk production in other species.

They discovered that platypus venom is a cocktail of proteins that originally had very different functions. Amazingly, the same proteins are found in reptile venom even though platypus and snake venom evolved independently.

They also found that the platypus has many more sex chromosomes than humans. Instead of just X and Y, the platypus has 10 sex chromosomes, with the gene sequences responsible for determining sex more similar to those in birds than in mammals.

“The platypus looks like such a strange blend of mammalian, bird-like and reptilian features and now we know that the genome is an equally bizarre mix of all of these,” said Ewan Birney, who led the genome analysis performed at the European Bioinformatics Institute.

“It’s much more of a mélange than anyone expected.”