Northern Isles residents are the most genetically distinct and have the highest levels of Norse DNA in Britain and Ireland, new research suggests.
Along with being genetically distinct, Shetland and Orkney are each other’s closest relatives, according to a wide-ranging new study.
People from Yell and the West Mainland were also found to have the highest levels of Norse DNA in Shetland.
The study, by the University of Edinburgh and the Royal College of Surgeons in Ireland, looked at the genetic makeup of more than 2,500 people from Britain and Ireland, including 1,000 from Scotland.
The Northern Isles had the highest levels of Norwegian ancestry outside of Scandinavia, with Shetlanders being 20 per cent Norse in their DNA. In Orkney the figure was 18 per cent while the next nearest is the Outer Hebrides at nine per cent.
One of the researchers was Jim Wilson, a professor of human genetics at the University of Edinburgh.
He said: “In both archipelagos it is incredible how clearly we can tell people apart using their DNA alone, in many cases right down to the level of the isle or parish.
“Within Shetland we can tell people apart from many different isles and districts using DNA alone.”
Within Shetland, many islands and areas have their own unique genetic identity, research has shown.
“Whalsay stands out,” said Prof Wilson, as the most distinct cluster within Shetland.
Yell also forms a cluster, which is closest to Unst.
Those with the highest level of Norse blood could be found in Yell and the West Mainland, reaching 28 per cent, while residents in Fair and Isle and Whalsay had the lowest — but still more than the Hebrides and parts of Orkney.
The distinctive nature in the isles can be attributed to Norse DNA, isolation and marrying locally within communities, districts and islands, giving Shetland its “distinction from the rest of the UK”.
The shortest distance where people could be separated by DNA alone was the short hop between Burra and the South Mainland, where genetics were “totally separate” from the isle to Quarff.
Before this genetics study “Shetland had not really been studied,” said Prof Wilson, with both Northern Isles having “by far and away the most distinct populations.”
The whole study is the result of a “decades worth of work,” said Prof Wilson.
Analysis focused on people with all four grandparents born in the same parish or isle, with this being the “last chance to capture this and understand some of these patterns”, according to Prof Wilson.
Many volunteers were born in the 1940s-1950s, taking the study back to the population structure of the Northern Isles in the 19th century.
“Some people are surprised that you can use DNA to show where people come from,” said Prof Wilson.
“It’s important for us to understand where in Britain and Ireland people are different genetically,” added Prof Wilson, as DNA-based medicine means it is important to represent “every corner” rather than just use samples from urban areas such as London or Edinburgh.
Studying different genes can help “equitable delivery of genetic medicine”, with this type of population analysis also potentially aiding in the discovery of rare DNA differences that might play major roles in human diseases.
“This work is important not only from the historical perspective but also for helping understand the role of genetic variation in human disease,” said Dr Edmund Gilbert, from the Royal College of Surgeons in Ireland.
“Understanding the fine-scale genetic structure of a population helps researchers better separate disease-causing genetic variation from that which occurs naturally in the British and Irish populations, but has little or no impact on disease risk.”
Prof Wilson also led the Viking Health Study which saw as many as 2,000 Shetlanders take a health check in 2014 in a bid to establish if there were genetic links to certain diseases, including multiple sclerosis.