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Wednesday, July 26, 2006

How Much R1b?

One of the outstanding questions from the halplogroup frequency estimation I did yesterday concerns the frequency of R1b.

Today I revisited the estimate, using the data from the Giacomo paper and a table of regional populations.

Now there are couple of limitations to this analysis. First, Giacomo didn't specifically measure R1b: he reports P*(x R1a). P is the parent of haplogroups Q and R, and so P is actually measuring the frequency of "true" P, Q, R1b, and R2. Undifferentiated P is fairly rare in Europe, but it exists in small amounts along with Q (except Q3, which is largely associated with Native American populations) and R2. Thus, the reported frequency of P*(xR1a) actually overstates the frequency of R1b by a little bit.

The second problem is that Giacomo did not report all other haplogroups, though I think he got all the major ones. Still, this will also cause the R1b proxy to skew a little high.

Anyway, using his data I estimated the P*(xR1a) frequency for each region and then took a weighted average using the regional population as the weight. I got a weighted frequency of about 45%, which means that (given the caveats above) I think the frequency of R1b in Italy is maybe 40-42%, or not far off the estimate I made yesterday.


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