PC analysis yielded a genetic map where the first two PCs highlight the genetic diversity corresponding to the Northwest to Southeast gradient and position the populations according to their approximate geographic origin. Our genetic map shows slightly different tendency from previously published ones in that the scatter plot takes the form of a triangle, with the Finnish, Baltic and Italian samples as its vertexes, and with Central Europe residing in its centre. The two PCs explain 8% and 4% of the genetic variability in the samples, which is almost twice as much as in previous European-based studies. This increase is likely due to the fact that the geographic coverage in our study has been broader and that our data captured more genetic variability (Figure 2).
