The Irish have far more Viking and Norman DNA than was previously thought, according to new research.
The research could lead to doctors being better able to diagnose illnesses, or even predict how suitable an organ donor might be for a patient.
The researchers discovered 23 genetic groups in Ireland, as well as 27 groups in England, Scotland and Wales.
The DNA map of Ireland shows considerable lasting contributions from the invasions of the Vikings, Normans and British.
Researchers compared mutations from almost 1,000 Irish genomes with over 6,000 from Britain and mainland Europe to find distinct Irish genetic clusters.
The clusters are separated by geography and were identified by comparing mutations in the genomes.
The DNA map showed the Irish genomes were more distinct in the west of the country than the East, which was to be expected as historically invasions of Ireland took place in the East.
The team noticed that the number of people with British ancestry dropped significantly in populations in the west.
They also detected genes from elsewhere in Europe and were able to calculate the timings of migrations of the Norse-Vikings and the Anglo-Normans and yield results that are consistent with historical records.
Co-author Professor Russell McLaughlin said: “Genes mirror geography in Britain and Ireland.
“Genetic data alone can virtually redraw a map of Britain and Ireland. It is interesting to note the exceptions to this rule.
“For example, some Scottish and Northern Irish people swap places, reflecting long-standing exchange of peoples between the two regions.
“Also, people from Orkney and Wales have retained some sort of ancient genetic identity that sets them apart from the expected patterns.”
The findings could give a fresh insight into treating genetic diseases.
The Irish have high rates of diseases such as cystic fibrosis, celiac disease, and galactosemia than other nationalities in Europe.
People in both Ireland and the UK are more likely to suffer from multiple sclerosis the further north in each country they live.
Geneticist Dr Ross Byrne, of Trinity College Dublin, said: “This subtle genetic structure within such a small country has implications for medical genetic association studies.
“As it stands current corrections for population structure in study designs may not adequately account for this within country variation, which may potentially lead to false positive results emerging.
“We feel this will be particularly important in the analysis of rare variants as these are expected to be less uniformly distributed throughout a country.
“We intend to explore this further and identify if this structure should be accounted for in corrections.”
Around 80 million people across the world claim Irish ancestry, with nearly half of those living in America.
However, the research shows that when it comes to genetics and the possible medical benefits of having a more precise knowledge of your DNA, it is worth learning more about yourself than simply being of Irish heritage.
With so many genetic groups, this information could become hugely important to know how or why some people are more vulnerable to certain illnesses than others.
The more detailed information would also be important if a person was ever in need of an organ transplant or skin graft.
The more genetically similar a person is to a donor, the lower the chance the body will reject the organ.
Written by Michael Kehoe @michaelcalling