mtDNA and the islands of the north atlantic: Estimating the proportions ofNorse and Gaelic ancestry

A total of 1,664 new mtDNA control-region sequences were analyzed in order to estimate Gaelic and Scandinavian matrilineal ancestry in the populations of Iceland, Orkney, the Western Isles, and the Isle of Skye and to investi gate other aspects of their genetic history. A relative excess of private l ineages in the Icelanders is indicative of isolation, whereas the scarcity of private lineages in Scottish island populations may be explained by rece nt gene flow and population decline. Differences in the frequencies of line age clusters are observed between the Scandinavian and the Gaelic source mt DNA pools, and, on a continent-wide basis, such differences between populat ions seem to be associated with geography. A multidimensional scaling analy sis of genetic distances, based on mtDNA lineage-cluster frequencies, group s the North Atlantic islanders with the Gaelic and the Scandinavian populat ions, whereas populations from the central, southern, and Baltic regions of Europe are arranged in clusters in broad agreement with their geographic l ocations. This pattern is highly significant, according to a Mantel correla tion between genetic and geographic distances (r = .716). Admixture analyse s indicate that the ancestral contributions of mtDNA lineages from Scandina via to the populations of Iceland, Orkney, the Western Isles, and the Isle of Skye are 37.5%, 35.5%, 11.5%, and 12.5%, respectively.