'Genetic map' of Britain shows legacy of war, migration

In an unprecedented probe into genetic history, scientists on Wednesday said native Britons have distinct DNA signatures that often correspond to their region's past.
People who have long-term ancestry in Britain fall into 17 "genetically distinct" regional clusters, they found.
The DNA heritage results from occupation or migration that occurred a thousand or two thousand years ago or more, yet has left a visible imprint in local DNA today, they said.
The study, published in the journal Nature, is the first detailed "genetic map" of any country.
"These researchers have been able to use modern genetic techniques to provide answers to the centuries-old question -- where we come from," said Michael Dunn of Britain's Wellcome Trust, a medical charity which funded the probe.
But "beyond the fascinating insights into our history, this information could prove very useful from a health perspective," Dunn suggested.
"Building a picture of population genetics at this scale may in future help us to design better studies to investigate disease."
The scientists unravelled the genetic code of 2,039 people who live in the rural United Kingdom and whose four grandparents were all born within 80 kilometres (50 miles) of each other.
Because a quarter of our genome comes from each of our grandparents, this effectively provided a genetic "snapshot" of the British population at around 1885, before the waves of immigration and urbanisation of the 20th century.
Without knowing the identities of the people whose DNA they analysed, the researchers looked at more than half a million sites in each genome, grouping together individuals who had similar telltales in their code.
The data was compared against DNA from 6,209 people in 10 countries in western Europe which, in ancient times, provided the source of Britain's migratory inflows.
From this, an intriguing picture emerged of subtle genetic variations around Britain today.
They often mirrored tribal groupings and kingdoms that existed in the country in the sixth century.
Contrary to popular belief, there is not one "Celtic" family for Scotland, Northern Ireland, Wales and Cornwall, the paper found.
In fact, inhabitants of these regions are among the most different from each other genetically.
The Cornish, for instance, were found to have more in common with other English groups than with the Welsh or Scots.
On the other hand, the famous rivalry between Cornwall and Devon is mirrored in genetic ID, with a division running almost exactly along the counties' common boundary.
In another curiosity, a 1,000-year-old cultural boundary called the Landsker Line, which divides English speakers from Welsh speakers in the southwestern Welsh county of Pembrokeshire, is also supported by genetic differences among people on either side of the line.
- Anglo-Saxon intermarriage -
Most of eastern, central and southern England comprises a mainly homogenous group where between 10 and 40 percent of genes can be traced to the Anglo-Saxons -- the first-millennium Germanic tribes who came to Britain after the fall of the Roman empire.
"This settles a historical controversy in showing that the Anglo-Saxons intermarried with, rather than replaced, the existing populations," the Wellcome Trust said.
People in the Orkneys, Scotland's far-north archipelago, are the most genetically distinct of the 17 "clusters."
A whopping 25 percent of their DNA comes from the Vikings.
Yet in the mainland UK, the Vikings have left no visible genetic signature, even though they ruled large parts of England from the ninth century.
The study brought together researchers from the University of Oxford, University College London and the Murdoch Childrens Research Institute in Australia.