Genetic markers and population history: Finland revisited

Abstract

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.

Figure 1

The map of Northern Europe and Finland showing the assessed sub-populations. The dark grey areas show the a priori assumed Early settlement area and the hatched line depicts the approximate position of the first political border between Sweden and Novgorod (Russia, year 1323).

Figure 2

Haplotype diversity point estimates in the Finnish (open and filled circles) and the European reference samples (open triangles), in a descending order. Above the axis: Y-STR (7 loci); below the axis: mtDNA HVS-I.

Figure 3

UPGMA clustering of sub-populations based on F_ST distances. The trees are drawn in the same scale.

Figure 4

MDS scatterplot based on the linearized Φ_ST estimates. (a) Seven-locus Y-STR haplotypes. (b) mtDNA HVS-I sequence data.

Figure 5

The magnitude of the Scandinavian gene flow in several primarily western Finnish sub-populations estimated from (a) the Y-STR data and (b) the mtDNA HVS-I+II data.