Putting flesh to the bones: A Homo neanderthalensis skull discovered in 1908 at la Chapelle aux saints, France.

Credit: Wikimedia

BERLIN: Another six months should yield the DNA key to the full Neanderthal genome, says Svante Pääbo and his team at the Max Planck Institute for Evolutionary Anthropology in Germany.

The team, based in Leipzig, is on schedule by the end of the year to sequence one full sweep, or about 3.8 billion base pairs of ancient Neanderthal nuclear DNA, Pääbo told a packed house full of researchers at the International Congress of Genetics in Berlin last week.

Delivering a full picture

Pääbo's team has already sequenced the 16-kilobase-long Neanderthal mitochondrial DNA genome some 35 times over. But, the nuclear sequencing is what will deliver the full picture about our closest extinct relative.

The experts hope it will shine light on exactly when modern humans diverged from the Neanderthals, whether modern humans came out of Africa or appeared in multiple regions, and what specifically makes us different from our ancient cousins.

Pääbo first announced the progress of his team at a Cold Spring Harbour Laboratory meeting in New York, U.S., in May. Last week he added that the 50 to 100-million-base-a-month sequence schedule had slipped a little between then and now, but that things are looking up.

Project results will be further outlined in an upcoming paper, tentatively scheduled for August in the journal Cell, Pääbo said.

Fascinating quest

The researchers pulled back the curtain on what's been a fascinating, years-long quest to map the genetic workings of the Neanderthal. They are doing so using 'pyrosequencing', a technique which handles several contiguous DNA sites in parallel. In this way the method is able to make sense of some of the degraded and broken pieces of DNA extracted from ancient fossil samples.

Even so, it's no easy matter, Pääbo told the crowd in Berlin. Sample contamination from bacteria and especially modern human DNA is constantly problematic – and since modern human DNA is close to Neanderthal, it makes definitive results a real challenge.

He said his team has examined 70 fossils from 16 different sites, and was able to find three with less than one per cent DNA contamination. These three are the Feldhofer source type, a 38,000-year-old male Neanderthal from Vindija, Croatia, and a set of nine 43,000-year-old Neanderthals – apparently victims of cannibalism – in a cave at El Sidron, Spain.

All the sequencing and analysis is being done in clean rooms and the team excavating El Sidron is using sterile suits and freezing samples as they work.