100,000 Year-old DNA Sequence Allows New Look At Neandertal's Genetic Diversity

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100,000 Year-old DNA Sequence Allows New Look At Neandertal's Genetic

Diversity

http://www.medicalnewstoday.com/medicalnews.php?newsid=44619

By recovering and sequencing intact DNA from an especially ancient

Neandertal specimen, researchers have found evidence suggesting that

the genetic diversity among Neandertals was higher than previously

thought. The findings also suggest that genetic diversity may have

been higher in earlier Neandertal periods relative to later periods

that approached the arrival of humans in Europe. Changes in genetic

diversity over time are thought to reflect population events, such as

low-population bottlenecks caused by disease or environmental change,

as well as the influence of random genetic change. The findings are

reported in the June 6th issue of Current Biology by a group of

researchers including Ludovic Orlando and led by Hänni of

Ecole Normale Supérieur in Lyon, France.

Neandertals were the only representatives of the genus Homo in Europe

during most of the last 300,000 years, becoming extinct shortly after

the arrival of modern humans on the continent around 30,000 years

ago. Traces of mitochondrial DNA (mtDNA) sequences still present in

fossilized bones have been used in past studies in an effort to

identify and track the potential genetic legacy of Neandertals among

modern Europeans. Though such genetic continuity would have been the

hallmark of interbreeding between modern humans and Neandertals at

the time of their European coexistence, the mtDNA sequences from the

nine neandertal specimens that have been analyzed to date - and that

lived around the time of the cohabitation period - do not match those

found among modern humans, suggesting that little, if any,

interbreeding took place.

In their new work, Dr. Hänni and colleagues now report the oldest

Neandertal mtDNA sequence ever recovered. The Neandertal specimen

analyzed consists in a molar of a 10-12 year-old child that lived in

the Meuse valley (Scladina cave, Belgium) around 100,000 years ago.

The specimen yielded 123bp of mtDNA - a very short section of DNA by

modern sequencing standards, but a technical feat considering the

very ancient source of tissue. The reason for choosing such an old

specimen was simple: it unambiguously predates the period when

Neandertals cohabited with modern humans. By comparing this sequence

with already published - and considerably younger - Neandertal

sequences, the researchers sought to reveal whether the Neandertal

mtDNA pool exhibited long-term stability or drastic modification

around the time of cohabitation with modern humans. There was a

second reason to pay attention on the Scladina molar: it has only

been discovered very recently. This means that all individuals who

have been in contact with it are known, and their DNA could be

sequenced to detect any possible contamination of the Neandertal

sample by modern human DNA.

The Neandertal sequence from Scladina confirms that Neandertals and

modern humans were only distant relatives - Neandertal sequences are

all closer to each other than to any known human sequence. But the

study also reveals that the genetic diversity of Neandertals has been

underestimated. Indeed, the mtDNA from the Scladina sample is more

divergent relative to modern humans than is mtDNA from recent

Neandertals, suggesting that Neandertals were a more genetically

diverse group than previously thought.