Mattingsdal (2020): The genetic structure of Norway

The genetic structure of Norway

Morten Mattingsdal, S. Sunna Ebenesersdóttir, Kristjan H. S. Moore, Ole A. Andreassen, Thomas F. Hansen, Thomas Werge, Ingrid Kockum, Tomas Olsson, Lars Alfredsson, Agnar Helgason, Kári Stefánsson, Eivind Hovig.

doi: https://doi.org/10.1101/2020.03.20.000299

Abstract:

The aim of the present study was to describe the genetic structure of the Norwegian population using genotypes from 6369 unrelated individuals with detailed information about places of residence. Using standard single marker- and haplotype-based approaches, we report evidence of two regions with distinctive patterns of genetic variation, one in the far northeast, and another in the south of Norway, as indicated by fixation indices, haplotype sharing, homozygosity and effective population size. We detect and quantify a component of Uralic Sami ancestry that is enriched in the North. On a finer scale, we find that rates of migration have been affected by topography like mountain ridges. In the broader Scandinavian context, we detect elevated relatedness between the mid- and northern border areas towards Sweden. The main finding of this study is that despite Norway’s long maritime history and as a former Danish territory, the region closest to mainland Europe in the south appears to have been the most isolated region in Norway, highlighting the open sea as a barrier to gene flow.

In particular:

The Sami people, and later immigrating minorities from Finland, like the “Kven” and “Skogfinner” (~1500 AD), are recognized ethnic minorities, and their influence on the genetic landscape of Norway is clearly detectable in the PCA, especially in the three northernmost counties (Figure 1 and Supplementary Figure S1). This is consistent with evidence from a health survey conducted in the 1980’s in Finnmark, where ~25% of the participants reported a Finnish family background. To fully appreciate the extent of Finnish and Sami ancestry, we quantified the extent of Asian ancestry per county (Supplementary Figure S1 & S2). We find a substantial extent of Asian ancestry (mean ~25%, Kautokeino), a size similar to that reported (42) in a single Sami sample (~25% Nganasan). To our knowledge, previous studies of the Sami in Finland report less Asian ancestry (~6%) (43), suggesting a more isolated Sami population in Norway.

I think it is becoming evident that the “Siberian” ancestry is found in the most isolated, ancestrally non-Uralic-speaking places, such as northernmost Scandinavia, the Arctic and the Tundra region, and Siberia all the way to Lake Baikal.

So it’s going to be interesting how some people will explain that the northward Saami expansion miraculously increased “Siberian” and decreased “Corded Ware” ancestry, instead of the opposite…

Homozygosity, measured as the summed length of homozygous segments detected by RefinedIBD, is relatively high in the north, presumably due to increased Sami and Finnish ancestry. Increased homozygosity is also evident in the border areas towards Sweden in the middle, and inland areas of mid-Norway, protruding down to the southwestern coast (Figure 3). Areas with substantially lower degrees of homozygosity include the Oslofjord area in the southeast, the Trondheimsfjord area in the middle, and the northern county of Nordland. The county of Nordland, with no major cities and home to large fishing grounds, appear heterogenous.