Planet Earth

Are Sardinians like Iberians?

Gene ExpressionBy Razib KhanFeb 29, 2012 3:32 AM

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Dienekes asks:

In terms of autosomal DNA, the Iceman clearly clusters with modern Sardinians, and also appears slightly more removed than them compared to continental Europeans. Interestingly, at least as far as the PC analyssi shows, Sardinians appear to be intermediate between the Iceman and SW Europeans, rather than Italians. Perhaps, this makes sense if the Paleo-Sardinian language is indeed related to languages of Iberia.

This trend aroused a little curiosity in me too. I'm sure Dienekes & company will be probing these issues a lot in the near future, but I couldn't wait. I took the IBS data set, which includes a lot of individuals from various areas of Spain, the Sardinians, French and French Basque from the HGDP, and the Tuscans from the HapMap, and threw them together into a pot. I added HGDP Russians & Orcadians (the latter a British group) to make sure there was a North European "outgroup." In terms of technical details the combined data set had ~220,000 SNPs, not too shabby. Additionally, I decided to run a PCA, where this number of SNPs is more than sufficient. On a technical note, the Sardinians were swamped in raw numbers by Iberians and Tuscans (over 100 and around 80 respectively). This means that the peculiarities of the Sardinian genetic heritage didn't show up, rather, what you see are the Sardinians as they arrange themselves in relation to the genetic variation of these more numerous groups. I used SmartPCA to generate the 10 largest independent dimensions of variation. To make a long story short there really wasn't much variation added from the second dimension on in this relatively homogeneous sample. So below is PC 1 and 2 (E1 and E2).

I'd be curious if someone could replicate this. I'm rather surprised that the Tuscans form such a tight cluster, but then again the IBS sample is very geographically distributed across Spain. The analogy to the HapMap Tuscans might be if Spain was represented by just Galicians. So what you're really seeing is a lot of Spanish variation, and of course the north-south range in Europe (which is really a southwest to northeast cline). I don't see a very strong affinity between Basques and Sardinians, but repeated trials indicated that the Sardinians do not cluster with Tuscans when it comes to their position within the Iberian genetic spectrum.

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