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Neandertal hot spots highlighted in modern humans' DNA: Stone Age people's mating with now-extinct species had both genetic pros and cons.

Humans appear to have inherited several traits related to skin, hair and some autoimmune diseases from Neandertal ancestors.

Two independent investigations identify for the first time the specific parts of the human genome that seem to have been most affected by Stone Age interbreeding with Neandertais. The research locates part of Neandertals' legacy in sections of present-day Europeans' and East Asians' DNA that are stocked with genes influencing the production of keratin, a key substance in skin, hair and nails.

By occasionally interbreeding with Neandertals after leaving Africa around 70,000 years ago, Stone Age humans inherited and retained keratin-related genes that must have aided survival outside of Africa, Sriram Sankararaman, a computational geneticist at Harvard Medical School, and his colleagues propose January 29 in Nature.

Neandertals' DNA contributions to modern humans also encompass genes related to several medical conditions, including lupus and Crohn's disease, Sankararaman's group says.

Neandertais lived in Europe and Asia between around 200,000 and 30,000 years ago. Previous studies estimated that 1 to 3 percent of non-Africans' DNA today comes from Neandertals, while present-day Africans have little or no Neandertal ancestry.

About 20 percent of the Neandertal genome shows up in various places in the DNA of living Europeans and East Asians, geneticists Benjamin Vernot and Joshua Akey of the University of Washington in Seattle conclude January 29 in Science.

These new reports represent "the first steps toward getting a genomic picture of the actual Neandertal individuals that mixed with modern humans," remarks paleogeneticist Mattias Jakobsson of Uppsala University in Sweden.

The genome of a Neandertal woman who lived about 50,000 years ago has already been sequenced (SN: 1/25/14, p. 17). The two research teams compared the ancient woman's genome with modern-day humans' DNA, using different statistical techniques. Future work will be able to use genomes from additional Neandertal fossils to home in on genes that modern humans inherited through particular instances of Stone Age interbreeding.

Sankararaman's team developed a method for calculating the probability that modern human gene variants and DNA segments containing multiple genes came from Neandertals. The researchers compared the Neandertal woman's genome with the DNA of 1,004 modern-day humans living in different parts of the world.

If, for instance, a European carried a gene variant found in the Neandertal but not in present-day West Africans, whose ancestors do not appear to have interbred with Neandertals, the researchers concluded that the gene variant probably originated in Neandertals.

In a genetic analysis of 379 Europeans and 286 East Asians, Vernot and Akey identified unusually long chains of gene variants that people probably inherited via Stone Age interbreeding, presumably from Neandertals. These Neandertal hot spots did not appear in the DNA of 13 West Africans.

Sankararaman's group found that far fewer signs of Neandertal ancestry appear on the X chromosome and along a stretch of DNA containing genes that affect the testicles than in other parts of modern humans' genomes. Genes that reduce male fertility tend to accumulate on the X chromosome when closely related species of modern animals interbreed, suggesting that such genes initially might have passed from Neandertals to humans before disappearing due to natural selection. Neandertal genes that compromised how the testicles work may have met the same fate.

The patterns of Neandertal DNA found in the human genome suggest that ancient populations interbred at least twice across Europe and Asia, Vernot and Akey say.

Still, large swaths of Europeans' and East Asians' genomes contain unexpectedly little Neandertal DNA, Akey says. "These regions potentially are a road map to finding genes that make us human."

Caption: Ancient interbreeding has left about 20 percent of the Neandertal genome (fossil of one shown) in the gene pool of modern Europeans and East Asians.


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Title Annotation:GENES & CELLS
Author:Bower, Bruce
Publication:Science News
Geographic Code:1USA
Date:Mar 8, 2014
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