On Feb. 28, European and American scientists, including Stanford School of Medicine genetics professor Carlos Bustamante, PhD, and senior research associate Peter Underhill, PhD, announced the sequencing of Otzis entire genome. It is the oldest human sample to undergo such an analysis. Postdoctoral scholars Andres Moreno-Estrada, PhD; Brenna Henn, PhD; and Martin Sikora, PhD, also worked on the study, which appeared in Nature Communications. High-throughput DNA sequencing was performed at Massachusetts-based Life Technologies Corp.

The sequence revealed some things impossible to learn by studying the body: the color of his eyes, for example, (brown) and the fact that he was likely lactose-intolerant. But more importantly, it also gave clues to where his ancestors lived and how humans may have migrated across Europe during the Copper Age, which started about 7,000 years ago. The answer surprised some people:

The Icemans ancestry most closely mirrors that of modern-day Sardinians, said Underhill, who, with Bustamante, came to the conclusion by analyzing the mummys Y chromosome. His lineage is very rare in mainland Europe only 1 percent or less share the same sequence but is rather frequent in northern Sardinia and southern Corsica.

Sardinia is the second-largest island in the Mediterranean Sea. It lies 120 miles west of Italys mainland and 7.5 miles south of the French island of Corsica.

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The mummy of the Iceman is kept in a refrigerated cell in the South Tyrol Museum of Archaeology. Credit: South Tyrol Museum of Archaeology

Obtaining and sequencing DNA from such an ancient source was challenging. Ancient DNA, which has been exposed to the elements for thousands of years, is plagued by contamination both from the environment and anyone who has handled Otzi since his discovery, said Timothy Harkins, PhD, of Life Technologies who led the sequencing effort. To limit contamination, researchers used a long needle to tap the inner part of the femur.

As it was, the researchers obtained only about 20 nanograms of genomic DNA for sequencing, which is hundreds of times less than the amount usually used for whole-genome sequencing of modern-day samples. From this, the scientists were able to identify about 2 million unique sequence variants for population studies. One small variation on the Y chromosome pointed researchers to Otzis island heritage.

The finding suggests two scenarios: either the mummys ancestors were once more prevalent in mainland Europe than they are now (and some unknown selection process caused them to die off everywhere but the island strongholds), or they actively immigrated to the mainland from the island. Because there is little archeological evidence of the large, rapid population change required in the first possibility, the Stanford researchers favor the second.

Its thought that Sardinia was first peopled about 11,000 years ago by sedentary hunter-gatherers, said Underhill. Some samples of volcanic glass, or obsidian, found in mainland Italy and southern France have been shown to come from Mount Arci in Sardinia. This implies that there were episodes of trading between the island and mainland. If so, the mummys ancestors could have arrived in Europe as traders.

Link:
Genetic analysis of ancient 'Iceman' mummy traces ancestry from Alps to Mediterranean isle

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