IF you ever wondered whether there was more to Scotland's east-west divide than a culture clash over the correct condiments for a fish supper, then genetic research appears to offer an answer.
Scientists studying the Y chromosomes of hundreds of Scottish males have discovered the rate of a key Celtic marker dating back to 6th Century Ireland is more than twice as common in the DNA of men in Glasgow and the west than Edinburgh and the east.
The data, which has been gathered over the past two years as part of the Scotland's DNA project, is helping to shed light on major ancestral differences between Scotland's regional populations.
One of the most significant discoveries to date is in the ratios of a marker known as R1b-M222, the 'Ancient Irish' marker. Men carrying this on their Y chromosome - it can be passed only from father to son - are all distant descendents of Niall Noigiallach, the first High King of Ireland who lived about 1500 years ago.
Current data shows it is present in the DNA of 12% of men living in west Scotland, against 5% in the east, a legacy of more than a millenia of Irish immigration.
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Markers refer to "errors in copying" when DNA is passed down the generations. Each of us inherit some six billion letters of DNA, three billion from each parent.
The unique sequence is made up of a combination of four letters: A, C, G and T, shorthand for the molecules adenine, cytosine, guanine and thymine.
However, occasionally, small mistakes occur in the code that might see letters switch places. This is known as a single nucleotide polymorphism - or marker.
Geneticists can trace these back to the time, place and, sometimes, even the person, where they occurred. This means an individual's DNA can be analysed for key markers that offer clues to their ancestry.
Since launching in 2011, scientists at the Melrose-based Scotland's DNA facility have compiled data from thousands of saliva samples submitted by Scots eager to trace their family history. The DNA is extracted from skin and blood cells found in saliva.
The findings are being made public today to coincide with DNA Day, commemorating the discovery of the double helix in 1953, and a drive by Scotland's DNA to attract more participants.
In particular, the researchers want to map the ratios of the Celtic markers, and determine whether men in the east are more likely to carry Germanic and Anglo-Saxon markers owing to the Anglian kingdom of Northumbria, which encompassed Edinburgh from the 7th to 10th centuries.
Dr Jim Wilson, a geneticist and the chief scientist behind the Scotland's DNA project, said: "The most interesting thing for me is we can now break these groups up into subgroups. You can split the M222 up into about 20 different subtypes.
"The fact we can do that is interesting because maybe we can home in on whether it is one subtype of M222 that is responsible for the difference between east and west or multiple. If it is one, that might help us understand more clearly when in history this difference occurred.
"But to do that accurately, we need a lot more samples."
The genetic picture is less distinct for women, possibly indicating increased movement and interbreeding creating more homogenous X chromosomes among Scotland's female population.
One discrepancy is the U4 marker, which first occurred in the Middle East but is now most common in Siberia. Nicknamed the 'Yenesei marker' after the Siberian river, it has been found at a rate of 3.9% among women in west Scotland and 1.5% in the east.
Mass immigration from Lithuania to Lanarkshire in the late 1800s could explain the pattern, but at the moment researchers are reluctant to put it down to more than chance.
"If you want me to bet on it, I think the U4 difference would go away if we had more samples," said Dr Wilson. "But that is all the more reason for people to come forward. At the moment I have the information I have, but I do not know whether this is a real ancestral difference or just a blip."