The analysis shows that the Anglo-Saxons were the only conquering force, around 400-500 AD, to substantially alter the country’s genetic makeup, with most white British people now owing almost 30% of their DNA to the ancestors of modern-day Germans. People living in southern and central England today typically share about 40% of their DNA with the French, 11% with the Danes and 9% with the Belgians, the study of more than 2,000 people found. The French contribution was not linked to the Norman invasion of 1066, however, but a previously unknown wave of migration to Britain some time after then end of the last Ice Age nearly 10,000 years ago.See also British Isles mapped out by genetic ancestry : Nature News & Comment:
Today, few Britons have ancestors from just one local region of the UK, so it is hard to identify patterns of genetic variation specific to any one place. But Donnelley and his team found 2,039 Britons of European ancestry who lived in rural areas and knew that their four grandparents were all born within 80-kilometres of each other. Since these volunteers’ DNA was a mosaic of their grandparents’, who themselves were to known be strongly linked to one British region in the late nineteenth century, Donnelley hoped to find genetic variation that clustered neatly with their grandparents' geographic location.
I was not surprised at the finding that most of the English had German ancestry, but what did surprise me was the differences between Cornwall, Devon and Somerset.