Researchers have published a landmark study, which provides the first fine-scale genetic map of the island of Ireland.
'The Irish DNA Atlas; Revealing Fine-Scale Population Structure and History within Ireland' has been published in the journal Scientific Reports.
Led by the Royal College of Surgeons in Ireland (RCSI) and the Genealogical Society of Ireland, it has revealed patterns of genetic similarity in 10 distinct clusters.
These are roughly aligned with the ancient provinces, as well as with major historical events - including the invasions of the Norse Vikings and the Ulster Plantations.
Population geneticists and genealogists collected DNA samples from 196 Irish people with four generations of ancestry linked to specific areas across the island.
Analyses revealed geographic clusters within Ireland: seven of Gaelic Irish ancestry, and three of shared British-Irish ancestry.
It found that prior to the mass movement of people in recent decades, there were numerous distinct genetic clusters found in specific regions.
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.
Researchers say this probably reflects the Ulster Plantations.
Two of the Gaelic clusters align with the boundaries of the province of Munster, and 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.
While there is evidence of continual, low-level migration between the north of Ireland and the south and west of Scotland.
'A sink of Celtic ancestry'
Researchers say these findings will help deliver on the vision of the new FutureNeuro Science Foundation Ireland Research Centre - which is seeking to improve the diagnosis of rare neurological disorders and personalise treatment.
Edmund Gilbert of the RCSI, first author on the paper, said: "Our work informs on Irish history; we have demonstrated that the structure emerging from genetic similarity within Ireland, mirrors historical kingdoms of Ireland, and that Ireland acts as a sink of 'Celtic' ancestry.
"Additionally, we find evidence of a west-Norwegian-like ancestry that we believe is a signature of the Norse Vikings.
"We also observe the impact of historical events such as the Ulster Plantations on the DNA of the people of Ireland."
Michael Merrigan from the Genealogical Society of Ireland is co-author on the paper.
He said: "For those interested in genealogy and Irish history, this study challenges many of our received narratives on the origins of the people of Ireland.
"We now get a clearer, scientifically based, map of the distribution and settlement of our ancestral groups across the island of Ireland.
"Historians and students of medieval Ireland have now a wonderful resource on the movements and interrelationships of our ancestor groups through their DNA.
"This opens up many new and very exciting research opportunities for many disciplines, especially, those researching the Irish medieval genealogies and the history of Irish clans/septs."