Wednesday, September 12, 2012

Denisovan Genome Sequenced

Scientists have just completed and published a complete (non-rough draft) genome of Denisovans, a recently-discovered hominin closely related to Neanderthals.  We only have two teeth and a finger bone from this evolutionary cousin, and the DNA samples are sparse, degraded, and of generally low quality; therefore, a new method was needed.  Instead of sequencing double-stranded "double helix"-form DNA, they first split the DNA into single strands, more than doubling the amount of DNA they could sequence.  This allowed for a sequenced genome that was nearly as good as those obtained from live humans.  

This newly-sequenced genome opens the door to all kinds of future research.  It has already been compared to genomes taken from many different ethnic groups, as well as a rough draft Neanderthal genome, allowing researchers to differentiate which genes were contributed by Neanderthals and which were contributed by Denisovans.  It seems that Denisovans have particularly contributed to the Papuan genome, while Neanderthals actually contributed more to East Asian and Native American genomes, despite living in Europe.  This suggests that Neanderthals, Denisovans, and homo sapiens sapiens might've interbred on various occasions - the details are still unclear.  Not everyone agrees that interbreeding occurred at all, though; one study published about a week before the Denisovan genome suggests that genetic diversity across ethnicities actually comes from the diversity in the original African population of modern humans.  Regardless, this sequenced genome is a huge step forward in the molecular study of human origins.

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