DNA map of Ireland reveals the Irish have Viking and Norman ancestry and are far more genetically diverse than previously thought
The Irish are much more genetically diverse than previously believed and have Viking and Norman ancestry - just like the English, according to new research.
A comprehensive DNA map of the people of the Emerald Isle has for the first time revealed lasting contributions from British, Scandinavian and French invasions.
Researchers have discovered 23 genetic 'groups' in Ireland and 27 groups in England, Scotland and Wales.
The findings are significant because they could be used in future studies to identify the genetics underlying various traits and diseases in specific regions.
An estimated 80 million people worldwide claim Irish descent - almost half of them Americans who regard it as their main ethnicity.
It has long been assumed this means the blood in their veins is Celtic - but geneticists now say the truth is much more complicated.
Researchers have found 50 distinct genetic clusters (classified into broader groups) in Ireland and Britain as shown by the key, shown top left. They are separated by colour based on region. For instance the SEE cluster, labelled in red and in South East England, represents a genetic group with largely Anglo Saxon Ancestry. Groups with largely Celtic ancestry include NLU (shown in yellow) NSC (green) and NWA (pink). Top right: A map shows how the groups are split around Britain and Ireland. Bottom: Each cross on the plotted graph represents an individual whose genes were sequenced for the study, and they are colour coded according to which cluster they belong to. They are positioned based on where in the UK they are from, with the grey lines showing latitude (PC1) and longitude (PC4)
Genetic differences in Ireland
In the 10,000 years since Stone Age cavemen first arrived, the Irish have established distinct cultural regions.
But previous studies had identified no clear genetic groups within the population.
Now researchers have found distinct Irish genetic clusters, separated by geography by comparing mutations from almost 1,000 Irish genomes with over 6,000 from Britain and mainland Europe.
These are most distinct in western Ireland, but less pronounced in the east, where historical migrations have erased the genetic variations.
When the researchers took into account genetic contributions from people with British ancestry, a clear trend arose, showing this input dropping off in populations to the west.
They also detected genes from Europe and calculated the timing of the historical migrations of the Norse-Vikings and the Anglo-Normans to Ireland, yielding dates consistent with historical records.
'Genes mirror geography in Britain and Ireland,' co-author Professor Russell McLaughlin told the MailOnline.
'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.'
What the map shows
The study paints a new and more complex picture of the genetic landscape of Ireland, and demonstrates the signatures that historical migrations have left on the modern Irish genome.
Historical migrations and invasions have led to traceable genetic footprints in certain groups across the UK and Ireland, for example ancestral influence in Irish genomes is best represented by modern Scandinavians and northern European, according to the study.
Each group shows evidence of different kinds of ancestry as follows:
- South Leinster (SLM, purple), Central Leinster (CLN, dark blue), Connacht (CNN, light green) and North Leinster/Ulster (NLU, yellow): The strongest signals of Viking ancestry were traced in south and central Leinster, followed by Connacht and north Leinster/Ulster. The researchers found evidence of a single-date, one-source mixing event overlapping with the historical period of the Viking invasion of Ireland.
- South East England (SEE, red): The South East England genetic group represents a genetic group with largely Anglo Saxon ancestry as a result of the Anglo-Saxon invasion.
- Ireland, Scotland, Wales, Cumbria (CUM, purple) and Cornwall (COR, orange: Anglo-Saxon ancestry is relatively low in these areas, which largely have Celtic ancestry.
There exists high genetic diversity amongst clusters from the west coast of Ireland, with this diversity declining eastwards.
The researchers wrote that this may be because the west of Ireland was largely unaffected by historical migration.
By contrast, increased gene flow and migration into and across the east coast of Ireland from neighbouring Britain has led to less distinct eastern Irish groups.
In another striking pattern, many Northern Irish genetic samples clustered with southern Scottish and northern English samples.
This may be due to several historical events, such as the major economic migration from Ireland in the 19th and 20th centuries, the settlement of Scottish farmers in Ireland following the 16th century Elizabethan conquest of Ireland, and the suspected Irish colonisation of Scotland in the 6th and 7th centuries.
Researchers have found 23 distinct Irish genetic clusters in Ireland and Britain. These are most distinct in western Ireland, but less pronounced in the east. In the stock image above, the many different territories making up the British Isles, including Ireland and the UK, can be seen
How this could help medical research
Their latest research has uncovered a previously hidden DNA landscape, shaped through geography and historical migrations.
The findings, published in the journal PLOS Genetics, could also shed fresh light on genetic diseases - and lead to better treatments.
In both the UK and Ireland, for example, prevalence of multiple sclerosis increases the further north you go.
And compared with the rest of Europe, the Irish have higher rates of cystic fibrosis, celiac disease, and galactosemia, a serious metabolic disorder that prevents the breakdown of sugars in dairy, legumes and organ meats.
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.'
The Vikings left their genetic footprint in Ireland when they invaded the island, launching their first attack in 795 AD by raiding an island monastery. Pictured is a view of Benwiskin Mountain at County Sligo in Ireland
Being able to link genetic information to geographic origins helps medical researchers design studies that consider how and why a person, or a group of people, may be affected by certain illnesses.
It is not good enough just to know you are Irish.
It could be useful to know your DNA has been influenced by a unique genetic subgroup from one part of Ulster.
Considering that something like 20 to 30 per cent of North Americans can claim Irish ancestry, this could have huge repercussions across the world.
If you need an organ transplant or skin graft, it could make a difference in how well your body accepts the tissue.
The more genetically different you are from the donor, the shorter the life of the transplant.
Rejections are lower when the recipient's genome and the donor's have fewer differences.
The Irish are much more genetically diverse than previously believed and have Viking and Norman ancestry - just like the English, according to new research. Pictured is a replica of a Viking boat towed on the river Thames past London's Houses of Parliament on April 15, 2014
Professor Russell McLaughlin added: 'The long and complex history of population dynamics in Ireland has left an indelible mark on the genomes of modern inhabitants of the island.
'We have shown that, using only genetic data, we can accurately reconstruct elements of this past and demonstrate a striking correlation between geographical provenance and genetic affinity.
'Understanding this fine-grained population structure is crucially important for ongoing and future studies of rare genetic variation in health and disease.'
The study follows research by the Royal College of Surgeons in Ireland and the Genealogical Society of Ireland, which found genetic evidence of Viking settlement for the first time.
That team found there were at least 10 distinct genetic clusters across the country, roughly aligned with the ancient provinces or kingdoms of Ireland.
They collected DNA samples from 196 Irish people whose eight great-grandparents were born within 31 miles (50km) of each other in Ireland.
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