Genetic evidence for a family-based Scandinavian settlement of Shetland and Orkney during the Viking periods

Abstract

The Viking age witnessed the expansion of Scandinavian invaders across much of northwestern Europe. While Scandinavian settlements had an enduring cultural impact on North Atlantic populations, the nature and extent of their genetic legacy in places such as Shetland and Orkney is not clear. In order to explore this question further, we have made an extensive survey of both Y-chromosomal and mitochondrial DNA (mtDNA) variation in the North Atlantic region. Our findings indicate an overall Scandinavian ancestry of E44% for Shetland and E30% for Orkney, with approximately equal contributions from Scandinavian male and female subjects in both cases. This contrasts with the situation for the Western Isles, where the overall Scandinavian ancestry is less (E15%) and where there is a disproportionately high contribution from Scandinavian males. In line with previous studies, we find that Iceland exhibits both the greatest overall amount of Scandinavian ancestry (55%) and the greatest discrepancy between Scandinavian male and female components. Our results suggest that while areas close to Scandinavia, such as Orkney and Shetland, may have been settled primarily by Scandinavian family groups, lone Scandinavian males, who later established families with female subjects from the British Isles, may have been prominent in areas more distant from their homeland. Heredity (2005) 95, 129-135.

Highly discrepant proportions of female and male Scandinavian and British Isles ancestry within the isolated population of the Faroe Islands

“…The significance of almost all pairwise comparisons of the exact test therefore suggests the detected population structure to be due to the differential distribution of individual haplotypes rather than to differences in the distribution of deep-rooted phylogenetic clades among populations. 19 The diversity statistics in Table 1 indicate 21 The Faroe Islands also appeared to have a substantially lower level of gene diversity than the other populations ( Table 1).…”

“…These populations were therefore grouped in the subsequent analyses. The past source population of the Northern and Western parts of the British Isles is represented by contemporary samples from Ireland and inland Scotland, 19 which were grouped for analytical purposes. Sequences from the Western Scottish isles and the neighbouring Isle of Skye were likewise grouped, and a total of eight populations were used in the subsequent analyses ( Figure 3).…”

“…For specific 'private haplotypes' not present in the source populations, this probability was derived from the relative frequency of the presumed founder haplotype, that is, the phylogenetically closest haplotypes in terms of mutational differences. 18,19 An average proportion of haplotypes assigned a Scandina- …”

“…The best fitting admixture model was found by searching through all possible admixture proportions from Z N ¼ 0 to 1 in intervals of 0.0001, where Z N represents the proportion of either Scandinavian or British Isles founders. Randomly selected Faroese haplotypes were assigned a probability 18,19 of Scandinavian or British Isles ancestry, determined by their relative frequency in the two source populations. For specific 'private haplotypes' not present in the source populations, this probability was derived from the relative frequency of the presumed founder haplotype, that is, the phylogenetically closest haplotypes in terms of mutational differences.…”

“…The two main focuses of this paper are to (i) assess the effect of genetic drift on shaping genetic diversity within the Faroese population, and (ii) to evaluate the genetic impact of Scandinavian versus British Isles female ancestors on the Faroese population and compare it with previous estimates of male ancestry based on Faroese Y-chromosomal data 20 applying identical methods. 19 Methods DNA samples were provided by 122 unrelated males whose grandmothers originated from various islands, thereby representing all major regions of the archipelago. These males were originally collected for a study of male ancestry proportions using Y-chromosomal markers on the Faroe Islands.…”