Scientists have finally managed to take an extensive look at the genetic makeup of one of the most famous beasts of the last ice age. This week, an international team of researchers reports using a new technology to sequence a staggering 13 million basepairs of both nuclear and mitochondrial DNA from a 27,000-year-old frozen Siberian mammoth. Also this week, another team reports using a souped-up version of more conventional methods to sequence a mammoth's entire mitochondrial genome.
Ancient DNA has always held the promise of a visit to a long-vanished world of extinct animals, plants, and even humans. Although researchers have sequenced bits of ancient DNA, most samples have been too damaged or contaminated for meaningful results. A sample retrieved from the 27,000-year-old mammoth was in much better shape. To obtain it, evolutionary geneticist Hendrik Poinar of McMaster University in Hamilton, Canada, took bone cores from a woolly mammoth found in Siberian permafrost. The very cold winters and short, cool, and dry summers in the region turned out to be ideal for preserving DNA.
Poinar sent the DNA-rich sample to genomicist Stephan C. Schuster at Pennsylvania State University, University Park, who is working with a new genome sequencer developed by a team at Stanford University and 454 Life Sciences Corp. of Branford, Connecticut (ScienceNOW, 4 August). This rapid, large-scale sequencing technology sidesteps the need to insert DNA into bacteria before amplifying and sequencing it, thus preventing amplification bias from copying large amounts of contaminant DNA from bacteria or humans.
Preliminary analysis shows that the mammoth was a female who shared 98.55% of her DNA with modern African elephants, the researchers report online this week in Science. But mammoths were apparently even closer kin to Asian elephants, according to a smaller study of 17,000 mitochondrial basepairs, coauthored by ancient DNA pioneer Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and published online today in Nature.
The technique used by Poinar's group was so productive that experts predict it will be used soon to sequence entire genomes of extinct animals. "The 'next generation' sequencer that was used [in the Science paper] will revolutionize the field of ancient DNA," says evolutionary biologist Blair Hedges of Pennsylvania State University, University Park. And Pääbo calls the nuclear DNA work "really great--the way forward in ancient DNA is to go for the nuclear genome with technologies like this."