Marking the first such report, the nearly complete nuclear genome sequence of an extinct animal — the woolly mammoth — is published in Nature this week.
After thousands of years of extinction, Stephan Schuster of Pennsylvania State University and colleagues in the USA and Russia have now used ancient DNA extracted from hair samples to reconstruct the nuclear genome sequence of the woolly mammoth, Mammuthus primigenius.
The samples used to piece together some 80% of this genomic jigsaw puzzle came from several woolly mammoth specimens that were preserved in permafrost, which is ideal for preserving uncontaminated DNA in hair. Bones are often used in ancient-DNA studies, but are prone to contamination by modern microbial DNA.
Comparison of the woolly mammoth genome with that of its modern cousin, the African elephant, show that both genomes are likely to be at least 40% larger than those of the fully sequenced placental mammals. Schuster and colleagues also estimate that the mammoth’s genome is 1.4 times bigger than the human genome.
In a related News and Views article, Michael Hofreiter of the Max Planck Institute for Evolutionary Anthropology, Germany, notes that although the draft genome is too fragmented and error-prone to allow standard genetic prediction, Schuster and colleagues have identified several protein-coding positions unique to the mammoth compared with 50 other vertebrate species. The functional consequences or adaptive value of these differences, however, await investigation.
Hofreiter also points out that in addition to demonstrating that it is possible to sequence the complete genome of extinct species and compare them with living animals, the woolly mammoth provides a rich resource for further research.
Indeed, as Schuster and colleagues note, this study shows that nuclear genome sequencing of extinct species can reveal population differences not evident from the fossil record, and it could even allow researchers to discover genetic factors that affect extinction.
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