Fascinating New Insight Into tzi The Iceman’s Genetic History

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http://www.scienceofwonder.org/fascinating-new-insight-into-tzi-the-icemans-genetic-history/

Discoveries keep pouring in about tzi, our favorite Copper Age mummy, telling us more about the Alpine Iceman than perhaps he even knew himself. But although his genome has been extensively probed, there has been an important question that scientists struggled to get to the bottom of: What happened to his mothers genetic line?

According to new research, while that of his father exists today, his maternal lineage is now extinct. This offers us new insight not only into his heritage but also the demographic changes that occurred in Europe some 5,000 years ago.

We know quite a bit about tzis paternal lineage already, lead author Valentina Coia told IFLScience. The point of this study was to reanalyze his mitochondrial DNA and compare this with modern populations.

Mitochondrial DNA (mtDNA) is sometimes referred to as our second genome, and unlike the DNA wound into our chromosomes, its only passed down the female line. Earlier analysis of the mummys whole genome revealed that his Y chromosome, only inherited from fathers, shows clear links with modern-day populations. But when his mtDNA was analyzed, scientists found that his mitochondrial haplogroup basically a population sharing a common ancestor, in this case down the maternal line was different to any found so far in living individuals.

This was an interesting find, as it could suggest that tzis maternal line is no longer in existence. However, at the time, data regarding the haplogroup from which tziswas thought to have branched off from K1 was scarce, meaning few samples were available for comparison. Importantly, only a few of the samples were from Europe, and none from the eastern Alps, which was where the 5,300-year-old Iceman was discovered.

We therefore wanted to analyze more samples in order to really understand the maternal line, Coia said. Could we not find this lineage because it is no longer present, or because of the small number of individuals investigated?

tzi, pictured, also has 61 tattoos. South Tyrol Museum of Archaeology/Eurac/Samadelli/Staschitz

Published in Scientific Reports, Coia and colleagues based at the European Academy of Bolzano/Bozen gathered a large worldwide dataset consisting of 1,077 haplogroup K1 individuals, including 42 that originated from the eastern Alps. After comparing his mtDNA with these samples, the researchers could not find any evidence for the existence of his mtDNA lineage in present-day populations, indicating it is either extinct today or extremely rare.

So what happened to this lineage, but not his paternal line? In an attempt to find out, the team compared both tzis mtDNA and Y chromosome with data available from ancient samples recovered from 14 different sites across Europe. This revealed that while his Y-chromosome line was the dominant lineage in these Neolithic samples, the maternal lineage was far less common during this ancient time, and likely only existed locally in the Alps.

The team therefore puts forward a scenario in which population expansion and large migrations into Europe around 5,000 years ago significantly altered the genetic structure of this region. So while his scarce maternal haplotype was eventually replaced by that of newcomers, his paternal line survived in isolated populations, such as those in Sardinia, and thus still exists today.

Source: Array

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