https://www.nature.com/articles/s415...0rTjU7HQ%3D%3D

Abstract

The extent of population structure within Ireland is largely unknown, as is the impact of historical migrations. Here we illustrate fine-scale genetic structure across Ireland that follows geographic boundaries and present evidence of admixture events into Ireland. Utilising the ‘Irish DNA Atlas’, a cohort (n = 194) of Irish individuals with four generations of ancestry linked to specific regions in Ireland, in combination with 2,039 individuals from the Peoples of the British Isles dataset, we show that the Irish population can be divided in 10 distinct geographically stratified genetic clusters; seven of ‘Gaelic’ Irish ancestry, and three of shared Irish-British ancestry. In addition we observe a major genetic barrier to the north of Ireland in Ulster. Using a reference of 6,760 European individuals and two ancient Irish genomes, we demonstrate high levels of North-West French-like and West Norwegian-like ancestry within Ireland. We show that that our ‘Gaelic’ Irish clusters present homogenous levels of ancient Irish ancestries. We additionally detect admixture events that provide evidence of Norse-Viking gene flow into Ireland, and reflect the Ulster Plantations. Our work informs both on Irish history, as well as the study of Mendelian and complex disease genetics involving populations of Irish ancestry.



http://www.rcsi.ie/index.jsp?n=110&p=100&a=11226

Key findings


That prior to the mass movement of people in recent decades, there were numerous distinct genetic clusters found in specific regions across Ireland.

Seven of those revealed so far are of ‘Gaelic’ Irish ancestry and describe the borders of either Irish Provinces or historical kingdoms.

The remaining three are of shared Irish-British ancestry, and are mostly found in the north of Ireland and probably reflect the Ulster Plantations.

Two of the ‘Gaelic’ clusters together align with the boundaries of the province of Munster, and individually are associated with the boundaries of the kingdoms of Dál Cais and the Eóganacht.

There are relatively high levels of North-West French-like (probably ‘Celtic’), and evidence of West Norwegian-like (probably Viking) ancestry within Ireland.

There is evidence of continual, low level migration between the north of Ireland and the south and west of Scotland.