Top Story: September 4, 2012

Tiny Bone, Millions of Genes

Screen shot 2012-09-04 at 2.43.36 PM

Denisovans were a species of human ancestors known only by a small pinky bone fossil and two teeth discovered in Siberia a few years ago.

As slight as these finds are, scientists know quite a bit about these ancient hominins. In 2010, a team of scientists isolated and sequenced DNA from that finger bone fragment and discovered that it belonged to a young girl of an extinct Homo species described as Denisovan—after the Denisova cave in Siberia where the remains were found.

Unfortunately, the sequencing wasn’t reliable enough to do further studies. ScienceNOW explains:

But these genomes were too low quality to produce a reliable catalog of differences. Part of the problem was that ancient DNA is fragmentary, and most of it breaks down into single strands after it is extracted from bone.

Enter Matthias Meyer, a postdoc from Germany who developed a new way of sequencing. His novel technique splits the DNA double helix so that each of its two strands can be used for sequencing. This allowed the same team of scientists to sequence every position in the Denisovan genome about 30 times over ensuring that each nucleotide was in the correct spot.

The technique provides 99.9% accuracy—a quality similar to genomes that have been determined from present-day humans!

The much-improved genome furthers our understanding of the 50,000 year-old individual and population. The young girl had brown hair, eyes and skin and the genetic variation of Denisovans was extremely low—suggesting their population was never very large for long periods of time.

In addition, studies of the genome enhance our comprehension of human evolution. They describe the divergence between Denisovans and modern-day humans and confirm that modern populations from the islands of southeastern Asia (like Papua New Guinea) share genes with the Denisovans.

“This research will help determine how it was that modern human populations came to expand dramatically in size as well as cultural complexity while archaic humans eventually dwindled in numbers and became physically extinct,” says study co-author Svante Pääbo.

The findings were published last week in Science.

Image: Max Planck Institute for Evolutionary Anthropology

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