at we were generating would be some of the ancient DNA we really were interested in. We were looking for the proverbial needle in the haystack," Rubin said. "It worked--among the expected lion's share of contaminants we recovered reasonable amounts of 40,000-year-old cave bear DNA and useful information from it. We were lucky in that we had a very powerful magnet in the form of industrial strength computing to tease out the interesting data from a hodgepodge of different DNAs."
It turned out that about 6 percent of the sequence from the sample yielded cave bear sequence -- the rest represented a mosaic of microbial contaminants. Nevertheless within that fraction, there was a range of genomic sequence types, including fragments of 21 genes, identified by comparing the cave bear sample to the complete dog genome sequence that exists in the public databases. Dogs and bears, which diverged some 50 million years ago, are 92 percent similar on the sequence level.
The samples of cave bear bones and teeth from the study were collected from two cave locations in Austria. Extinct for more than 10,000 years, these particular cave bears, Ursus spelaeus, whose remains are found in abundance, were related to the ancestors of modern brown bears and polar bears. Fossil and cave-painting evidence supports that ancient humans interacted with the cave bears.
"When people hear about our success, they immediately think about how this strategy could work for dinosaurs," Rubin said. Barring some fundamental misunderstanding about the nature of DNA decay, he says it is highly unlikely viable DNA will be recovered from 150 to 200 million year old Jurassic age samples.
Currently, the theoretical limit is about 100,000 years old for samples preserved in the same conditions that the cave bear specimens where found -- relatively dry, high altitude, with moderate temperatures--or if frozen, perhaps longer.
"We picked cave bear as an initial test cPage: 1 2 3 4 Related biology news :1
Contact: David E. Gilbert
DOE/Joint Genome Institute
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