Friday, January 15, 2016

DNA sequencing reveals the fate of Ötzi the Iceman

Today in Scientific Reports, researchers from the European Academy of Bolzano/Bozen (EURAC) have reported on the fate, and ultimate extinction, of Ötzi the Iceman’s maternal genetic lineage. With these new insights the fates of both Ötzi’s maternal and paternal genomes have been conclusively revealed.

Ever since Ötzi’s body was discovered in 1991, scientists have sought to understand not only who he was and how he lived, but also where he lay within Europe’s genetic history. Although the sequence of Otzi’s mitochondrial genome was published in 2008, and his nuclear genomic sequence was reported in 2012, several questions remained unanswered.

The Iceman. Image source: © EURAC/Marion Lafogler

When Ötzi’s mitochondrial genome was sequenced in 2008, scientists showed that it belonged to the relatively broad K1 mitochondrial genetic lineage. More specifically, Ötzi’s maternal genetic lineage was referred to as K1f. The authors had compared the Iceman’s mitochondrial genomic sequence to modern samples, hoping to identify any traces of the K1f mitochondrial lineage within the modern population. However, a relatively limited set of modern samples hampered their ability to conclusively uncover Ötzi’s maternal genomic signature within the modern humans of today. Traces of the K1f lineage could have been absent from the samples in 2008, either because the sample size was too small, or because the K1f genetic line had gone extinct.

According to Valentina Coia, first author of this most recent study “The first hypothesis could not be ruled out given that the study considered only 85 modern comparison samples from the K1 lineage – the genetic lineage that also includes that of Ötzi – which comprised few samples from Europe and especially none from the eastern Alps, which are home to populations that presumably have a genetic continuity with the Iceman. To test the two hypotheses, we needed to compare Ötzi’s mitochondrial DNA with a larger number of modern samples.”

“To test the two hypotheses, we needed to compare Ötzi’s mitochondrial DNA with a larger number of modern samples.”

In order to confirm the extinction of Ötzi’s maternal genetic line, Coia and her colleagues examined the DNA of 1,077 individuals including members of Ötzi’s broader K1 lineage, as well as individuals descending from similar genetic lineages. Despite the relatively large set of samples studied, the research teams were unable to uncover evidence of the Iceman’s K1f maternal genetic lineage, or even genetically close lineages, within the modern population.

Though Ötzi’s maternal genetic lineage appears to be extinct, his descendants live on. In 2013, DNA testing of blood samples taken from the Tyrol region of Austria identified 19 men that appear to be genetic descendants of Ötzi. Publishing today in Scientific Reports, Coia and her colleagues further pursued exploring the history of Ötzi’s paternal genetic line, which endures within Europe today. By comparing DNA results from their modern samples, as well as genetic samples taken from 14 different European archaeological sites, the researchers have developed a working hypothesis for the ultimate fates of Ötzi’s maternal and paternal genomes. The researchers believe that members of Ötzi’s paternal lineage arrived in Europe from the Near East approximately 8,000 years ago. At some point following this migration, they believe that Ötzi’s paternal lineage was replaced in most of Europe, remaining only in isolated regions including Sardinia. In contrast to the relatively geographically diverse members of Ötzi’s paternal lineage, Coia and her colleagues suggest that members of Ötzi’s maternal line were a relatively small population remaining geographically isolated and stationary. Ultimately, the authors believe that the same migrations that displaced the Iceman’s paternal ancestors in much of Europe ultimately displaced, and rendered extinct, Ötzi’s maternal line.

Teresa-Lynn Martin | Meta Science Fellow

Featured image: South Tyrol Museum of Archaeology/EURAC/M.Lafogler
This story was prepared with materials provided by the European Academy of Bolzano/Bozen (EURAC).



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