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The Finnish population in Northern Europe has been a target of extensive genetic studies during the last decades. The population is considered as a homogeneous isolate, well suited for gene mapping studies because of its reduced diversity and homogeneity. However, several studies have shown substantial differences between the eastern and western parts of the country, especially in the male-mediated Y chromosome. This divergence is evident in non-neutral genetic variation also and it is usually explained to stem from founder effects occurring in the settlement of eastern Finland as late as in the 16th century. Here, we have reassessed this population historical scenario using Y-chromosomal, mitochondrial and autosomal markers and geographical sampling covering entire Finland. The obtained results suggest substantial Scandinavian gene flow into south-western, but not into the eastern, Finland. Male-biased Scandinavian gene flow into the south-western parts of the country would plausibly explain the large inter-regional differences observed in the Y-chromosome, and the relative homogeneity in the mitochondrial and autosomal data. On the basis of these results, we suggest that the expression of 'Finnish Disease Heritage' illnesses, more common in the eastern/north-eastern Finland, stems from long-term drift, rather than from relatively recent founder effects.

Northwest Siberia is geographically remote territory, which has been settled by indigenous human populations probably since the Upper Paleolithic. To investigate the genetic landscape of Northwest Siberians, we have analyzed mitochondrial and Y chromosome DNA polymorphisms of 169 unrelated individuals from Khanty and Mansi ethnic groups in Northwest Siberia. In addition, HVS-I sequences (N = 3522) and Y chromosome SNP data (N = 2175), obtained from the literature, were used to elucidate the genetic relationships among the North Eurasian populations. The results show clinal distributions of mtDNA and Y chromosome haplogroups along East-West axis of Northern Eurasia. In this context, the Ugric-speaking Khanty and Mansi appear as unique intermediate populations carrying Upper Paleolithic and more recent haplotypes typical for both West and East Eurasian gene pools. This admixture indicates that the Khanty and Mansi populations have resided in the contact zone of genetically distinguishable eastern and western Eurasia.