Genetic diversity shrinks in UK-study

LONDON, Aug 2 (Reuters) Britons are less genetically diverse today than 1,000 years ago, according to a study that could offer clues to why some people survive disease better than others.

An explanation for the loss of diversity could lie in plagues in the 14th and 17th centuries, said Rus Hoelzel, a population geneticist at Durham University who together with co-authors published the findings in Biology Letters.

The lower diversity is surprising because people from all over the world and from different ethnic backgrounds have settled in modern-day Britain, he said.

''Based on the assumption that modern England is more cosmopolitan, higher genetic diversity in the ancient sample was unexpected,'' Hoelzel said in a telephone interview on Wednesday.

''The expectation is that the gene pool should be more mixed.'' The researchers said mitochondrial DNA extracted from 48 ancient people used in the study were also more diverse than those found in modern populations in northern Germany, Denmark and Norway. These areas provided the likely source of migrants to England at the time.

The team used mitochondrial DNA because it is passed on from mother to daughter virtually unaltered and represents a powerful way to track human lineage.

The genetic material came from ancient Britons who lived between AD 300 and 1000, and also included 6,320 modern-day mitochondrial DNA samples from England, Europe and the Middle East.

The Black Death between 1347-1351 wiped out as much as 50 percent of Europe's population while the Great Plague of 1665-1666 killed a fifth of London's residents, the authors noted in the study.

Hoelzel said the plagues did not affect everybody the same way, so some families may have left more daughters to reproduce and pass on their genes.

In other cases the deaths of whole villages where many people would have been related could have wiped out entire lineages.

''If some families survived better, they are going to displace other families and there will be less diversity overall,'' Hoelzel said.

If natural selection played a role, these findings could one day help scientists pinpoint genes that make some people more resistant to certain diseases, Hoelzel said.

''It would be important if you could identify a new gene that is important in protecting people against future pandemics,'' Hoelzel said.

Reuters CS GC0954