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Iceman's Genetic Ties to Sardinian Population Offers Hints About Agriculture's Ancient Spread

SAN FRANCISCO (GenomeWeb News) – By delving into the genetic relationship between the Tyrolean Iceman and present-day European populations, researchers from the US, Italy, and Germany believe they have new clues about an ancient population that brought agriculture to Europe.

Martin Sikora, a post-doctoral researcher in Carlos Bustamante's Stanford University genetics lab, described the effort during a session on admixture and demography at the American Society of Human Genetics annual meeting here yesterday afternoon.

Sikora and his colleagues used SNP and whole-genome sequencing datasets to garner genetic evidence supporting the notion that the 5,300 year old Tyrolean Iceman, nicknamed Ötzi, shared ancestors with present-day populations living in Sardinia. But he was not alone in that respect, results of their analyses suggest.

The team found that an ancient Swedish farmer sequenced by a Swedish and Danish team earlier this year also clustered genetically with the Sardinians. So, too, did an ancient Bulgarian individual.

On the other hand, Sikora explained, a Swedish hunter-gatherer sequenced by the Swedish and Danish team and another ancient hunter-gatherer from Iberia clustered more closely with northern European populations.

Together, such results suggest that the Tyrolean Iceman and his ancient agricultural counterparts in Europe may have been part of a relatively widespread genetic group in Europe — perhaps reflecting the genetics of individuals who brought agriculture to Europe from the Middle East.

If so, Sikora explained, the relatively isolated Sardinian population could theoretically have remained more genetically similar to this ancestral group than populations in other parts of Europe that went on to mix with hunter-gatherers and other populations.

Results of the study also indicate that Ötzi was part of a larger population living in Europe, rather than a Sardinian son who had traveled far from a southern European site to reach the Alps.

"Our results show that the Tyrolean Iceman was not a recent migrant from Sardinia," Sikora and his co-authors wrote in the abstract provided for the ASHG talk, "but rather that among contemporary Europeans, Sardinians represent the population most closely related to populations present in the Southern Alpine region around 5,000 years ago."

Ötzi's mummified, frozen remains were discovered on an alpine glacier near the Italian-Austrian border in 1991. And when the Iceman's genome was described in Nature Communications early this year, authors of the study noted that he appeared to share genetic features with present-day populations in Sardinia, a relatively isolated island in the Mediterranean Sea.

As a follow-up to that work, researchers decided to take a closer look at that apparent genetic relationship. In particular, Sikora said, they were interested in determining whether Ötzi was, indeed, more closely related to Sardinians than to other European populations and, if so, the implications of this relationship.

For their analyses, the researchers first turned to Human Genome Diversity Panel data representing tens of thousands of SNPs genotyped in 943 individuals using the Affymetrix Axiom Human Origins array.

After determining how existing populations clustered, the team considered data for Ötzi and the four other ancient individuals: a Swedish hunter-gatherer and a Swedish farmer, both estimated to be around 5,000 years old, an ancient Iberian hunter-gatherer, and a Bulgarian farmer believed to be from the early Iron Age.

Both farmers clustered genetically with the present-day Sardinian population using the SNP data, Sikora said, while the hunter-gatherers appear to be more genetically close to northern Europeans.

Likewise, when the researchers compared the Iceman genome with data from the 1000 Genomes Project data, publicly available genomes produced by Complete Genomics, and unpublished low-coverage genome sequence data for 452 individuals from Sardinia, their results further shored up the assertion that Ötzi is more closely related to Sardinians than to present-day populations from other parts of the world.

Once again, available data for the other ancient individuals seemed to suggest that this genetic relatedness was also present amongst at least some of the individuals practicing agricultural lifestyles in other parts of Europe.