Woolly Mammoth Genome Sequenced

Scientists at Penn State are leaders of a team that is the first to report the genome-wide sequence of an extinct animal, according to Webb Miller, professor of biology and of computer science and engineering and one of the project's two leaders. The scientists sequenced the genome of the woolly mammoth, an extinct species of elephant that was adapted to living in the cold environment of the northern hemisphere. They sequenced four billion DNA bases using next-generation DNA-sequencing instruments and a novel approach that reads ancient DNA highly efficiently.

"Previous studies on extinct organisms have generated only small amounts of data," said Stephan C. Schuster, Penn State professor of biochemistry and molecular biology and the project's other leader. "Our dataset is 100 times more extensive than any other published dataset for an extinct species, demonstrating that ancient DNA studies can be brought up to the same level as modern genome projects."

The researchers suspect that the full woolly-mammoth genome is over four-billion DNA bases, which they believe is the size of the modern-day African elephant's genome. Although their dataset consists of more than four-billion DNA bases, only 3.3 billion of them -- a little over the size of the human genome -- currently can be assigned to the mammoth genome. Some of the remaining DNA bases may belong to the mammoth, but others could belong to other organisms, like bacteria and fungi, from the surrounding environment that had contaminated the sample. The team used a draft version of the African elephant's genome, which currently is being generated by scientists at the Broad Institute of MIT and Harvard, to distinguish those sequences that truly belong to the mammoth from possible contaminants.

"Only after the genome of the African elephant has been completed will we be able to make a final assessment about how much of the full woolly-mammoth genome we have sequenced," said Miller. The team plans to finish sequencing the woolly mammoth's genome when the project receives additional funding.

The team sequenced the mammoth's nuclear genome using DNA extracted from the hairs of a mammoth mummy that had been buried in the Siberian permafrost for 20,000 years and a second mammoth mummy that is at least 60,000-years-old. By using hair, the scientists avoided problems that have bedeviled the sequencing of ancient DNA from bones because DNA from bacteria and fungi, which always are associated with ancient DNA, can more easily be removed from hair than from bones. Another advantage of using hair is that less damage occurs to ancient DNA in hair because the hair shaft encases the remnant DNA like a biological plastic, thus protecting it from degradation and exposure to the elements.

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