The genetics of the UK population

24 March 2015

Interview with

Garrett Hellenthal, UCL

Who do you think you are? Tracing your family history is becoming more and more popular, but as well as digging through dusty parish records, our genes can tell us a lot about where we've come from. Now a major new study has used genetic analysis to look at the ancestry of British people, Dnahelix_genetic_fingerprintshowing that different parts of the UK seem to harbour their own distinctive genetic flavour and helping to reveal where some of these groups might have originated from, hundreds of years ago. UCL's Garrett Hellenthal, who was part of the study, explained how he and his colleagues traced our country's family tree.

Garrett - We sampled some 2,000 individuals from across the United Kingdom. There was a requirement for each individual; all 4 of their grandparents are to be born within 80km from one another. So, trying to get individuals that have been living in a region for a while so we can get a snapshot of older history and void recent migration. And the aim of the study - so, two major things that we did - one was to see if we can cluster individuals based solely on looking at their genetics and seeing that for example, individuals that were sampled from one part of the United Kingdom, are they more similar to each other than they are to individuals sampled from another part of the United Kingdom. And how does this correlate with kind of known boundaries in history. The second thing was to take the DNA of these same individuals and compare them to some 6,000 individuals from across continental Europe and identify if different parts of the UK, share matching DNA patterns with different parts of Europe. And if so, do those correlate with known migrations from Europe and of all the migrations from Europe into the UK which have kind of had the biggest genetic impact in the people in the UK today?

Kat - Tell me some stories about us. What have you found?

Garrett - Just by comparing DNA of individuals in the UK to each other, there was kind of a striking correlation - it turns out - with genetics and geography, to the point which we can tell whether an individual came from Cornwall which is in the southwest of England versus whether they were sampled from one county over in Devon. Genetically, we can tell them apart which is quite surprising because geographically, those are quite nearby regions. In fact, the difference between the two groups seems to be separated largely along modern day county borders which is another sort of interesting finding. But then at the same time, there's some parts of the UK and for example, central south and eastern England, individual sample from across very large swath of those areas, all were genetically very homogenous. We couldn't really tell them apart, suggesting that there had been quite a bit of movement and intermixing along those regions. And so then when we try to take the DNA of these individuals and compare them to Europe to learn about why we're observing these sorts of pockets of genetics across the United Kingdom, we found that one of the bigger stories in UK history appears to be the Anglo-Saxon migrations. So, UK has a very strong history, lots of migrations. For example, the Romans occupied big parts of England for about 400 years until about the 5th century. And yet despite that they've built lots of walls and baths and other things that you can see across England today. But in spite of that, there seems to be very little genetic impact at all related to the Roman Empire as far as we can tell.

Kat - They didn't fancy us basically.

Garrett - Yeah. It is believed that they didn't really migrate here in large numbers. Perhaps it was difficult to convince people to leave the Mediterranean and come up to the UK. In contrast to that, after the fall of the Roman Empire, that kick started what were known as the Anglo-Saxon migration's in the 5th and 6th centuries. And for those migrations, there's large scale migrations from places in modern-day Denmark and northwest Germany who settled into a big area within southeast England. It was unknown amongst archaeologists as to whether the Anglo-Saxons completely displaced the people that were there so that if you looked at an Englishman today, basically, they'd be entirely Anglo-Saxon in heritage or whether they intermixed with the inhabitants that were there. And so, what our study threw up was that they appeared to have intermixed. If you look at an Englishman today on average in these regions, this area of the southeast England, they have about 10% to 40% of their DNA that seems to trace to these Anglo-Saxon migrations. And the rest seems to be similar to other areas of the UK, which we think of as the kind of pre-Saxon inhabitants.

Kat - There's quite a lot in the news about immigration coming into the British Isles. Do you feel that when you look at the genetic history of the people who live here that this has been going on for many, many years?

Garrett - Yeah, that's right. One of the things that I've found in my studies is that every group appears to be mixtures of other groups. So we basically all descend from this sort of passing or mixing events. Human populations, clearly, once we expanded across the globe, we didn't just stay put. We went back out again and intermixed. And so, you see these signals everywhere. It's a constant interaction amongst different groups and that's still continuing today and will for a long time.

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