Neanderthal Bone Yields Complete Mitochondrial Genome

Aug. 7, 2008 -- DNA extracted from a 38,000-year-old Neanderthal bone has just enabled scientists to sequence the complete mitochondrial genome for the human-like species, according to a paper that will be published tomorrow in the journal Cell.

The remarkable feat, which has led to at least three major discoveries about the extinct stocky European individuals, represents a breakthrough for studies on the human family.

"This is the first complete mitochondrial genome sequence from an extinct hominid," lead author Richard Green explained to Discovery News.

Mitochondria, which an individual inherits from his or her mother, are cellular powerhouses that possess their own DNA and include 13 protein-coding genes. The researchers sequenced the Neanderthal mitochondria 35 times to ensure their findings were as accurate as possible.

After studying the newly completed genome, Green, a researcher at the Max-Planck Institute for Evolutionary Anthropology in Germany, and his team first concluded that the Neanderthal mitochondria falls outside the range of variation found in humans today, offering no evidence that interbreeding occurred between them and us.

The researchers are quick to add that such interbreeding could still have happened and that the Neanderthals' "exact relationship with modern humans remains a topic of debate."

Clearer is the fact that Neanderthals and humans split from a common ancestor around 660,000 years ago. The researchers based this initially upon prior research that determined humans and chimpanzees diverged from each other six to eight million years ago.

They calculated mtDNA sequence changes for both humans and Neanderthals since that time. These accumulated changes then "let us calculate how long ago was the most recent common ancestor of humans and Neanderthals," Green said.

He added, "This common ancestor likely looked something like Homo erectus." This extinct hominid is believed to have been super strong with a relatively large head and brain.

What most surprised the scientists was how little purification acted upon the Neanderthal's DNA, meaning that the elimination of slightly deleterious alleles, or variant gene forms, didn't occur very often within the population.