DNA used to pinpoint ancestors' villages

An individual's genome can be used to accurately predict their ancestral origin, to the nearest five miles, a new study has found.

James Wilson and colleagues at the University of Edinburgh, Scotland, studied the genomes of 250 people from neighbouring communities in Italy (57), Croatia (157) and Scotland (36). They selected people whose four grandparents originated 'from the same valley, village or isle', to ensure that each person had a single place of origin.

Using their genetic information - genome-wide scans of 300,000 SNPs (single nucleotide polymorphisms) for each person- they were able to correctly predict the village of origin in 100 per cent of Italian, 96 per cent of Scottish and 89 per cent of Croatian people. The study was published in the European Journal of Human Genetics.

The researchers excluded first, second and third degree relatives from the study, so that no study participants were related to each other. This allowed the researchers to focus on the genetic patterning arising from people's shared ancestry, and control for more recent patterning arising from family structures and partner choice over the past 120 years.

The authors commented that predicting the village origin in the Croatian population was the least accurate because the villages were the closest together geographically - only eight kilometres - and were not separated by any large physical barriers. The villages studied in Scotland and Italy, by contrast, were separated by 15-30 km of sea and large mountain ranges, respectively.

The authors conclude that their results are further evidence that the choice of human partners over several millennia is very structured and 'highly nonrandom'.

'This exciting finding begs the question of whether we will be able to identify the rural origins of urban people with ancestry from many places across a country', said Wilson, adding: 'It might be possible to take mixed urban individuals and work out which parts of their genome came from which rural places'.

In a related study, published in the same journal, O'Dushlaine and colleagues used genome-wide association data from Irish, British, Swedish, Portuguese and Bulgarian populations to identify patterns of human genetic variation across and among different European populations. The researchers used four methods of analysing the genetic information and kinship within the populations: population genetic structure, linkage analysis, homozygosity and genetic diversity.

They found that genetic diversity across Britain and Ireland is lower than in mainland Europe, but that a 'subtle genetic structure' exists in this region despite its relatively homogenous nature. They confirmed that the Scottish population was more similar genetically to the English than the Irish, and observed a 'diversity gradient' across Britain and Ireland, where genetic diversity was highest in southern England and lowest in Ireland.

The researchers suggest that the diversity gradient across Britain and Ireland supports the serial founder effect theory of human migration, where 'population expansion involves successive migration of a small fraction of individuals out of the previous location, starting from a single origin in sub-Saharan Africa'. Ireland, isolated and at the edge of the Atlantic, was one of the last regions of Europe to be populated by humans and consequently has the lowest genetic diversity.

Not only geography, but also recent history, may be reflected in genomic data, the authors suggest. For example, famine and mass emigration, a primarily agricultural society, less extensive industrialisation and urbanisation, and the preservation of traditional Gaelic family structures have all contributed to the low genetic diversity observed in Ireland.

Both of these studies highlight how population genetics can illuminate and offer a different perspective into human history. These genetic studies give insight into the local social and family structures of populations in Britain and Europe, and confirm the very small geographical ranges of these past communities, which have been maintained up to the present in more rural areas of Europe.