Population structure in Ireland and Britain

From the paper:

Eigensoft PCA analysis across all seven of our European and European-ancestry populations broadly identified four sub-groups consisting of (i) Bulgarian, (ii) Portuguese, (iii) Swedish and (iv) Irish/British/Utah populations (see Figure 1a, Supplementary Figure S1). The first two principal components (PCs) separate out northern from southern, and western from eastern European ancestry, respectively.

The Europe-wide PCA analysis positions the Scottish population (Aberdeen) intermediate between the Irish and English populations. We further explored this observation by restricting our PC analysis to residents of Ireland, Scotland (Aberdeen) and south/southeast England (Figure 1b, Supplementary Figure S1). This analysis confirms the observation that the Scottish population is intermediate between the Irish and English cohorts on the first principal component(this time dividing west from east). Although more subtle, the Scottish cohort is also shifted slightly from the other two on PC2.

The distinction between Britons and Swedes was also noted in an earlier study. It's nice to see Bulgarians and Portuguese sampled, as they have been rather neglected in genomic studies, but, unfortunately none of their neighbors or any other intermediate populations were included, which is understandable as the study focused on British Isles populations. Bulgarians and Portuguese served as "anchor points" to re-create the well-known correlation of the first two PCs of European genetic variation with longitude/latitude.

The intermediate position of Scottish populations relative to the Irish and English is not surprising, given the Gaelic connection between Scotland and Ireland.

The paper also has haplotype diversity data that can be compared with those recently published by Auton et al.

In summary, our results illustrate a subtle genetic structure across Britain and Ireland in the context of the comparatively homogenous nature of the European genetic pool. We have observed slightly elevated levels of LD and genome-wide homozygosity in Ireland and Sweden compared with neighbouring British and European populations, although these levels do not approach those of traditional population isolates. Similarly, we have illustrated a decrease in HD in Britain and Ireland, more so in Scotland and Ireland than in England.

Finally, the authors present results of frappe analysis (Figure S2):

European Journal of Human Genetics - Abstract of article: Population structure and genome-wide patterns of variation in Ireland and Britain

Dienekes' Anthropology Blog: Population structure in Ireland and Britain (O'Dushlaine et al. 2010)