Within a drop of blood, you can find all the information you need to reasonably guess where a person came from, without ever having to look at their face, name or passport. Small variations in our DNA are enough for the task. They can be used to pinpoint someone's place of origin to a remarkable degree of accuracy, often to within a few hundred kilometres.
The new discovery comes from a team of Swiss and American researchers led by John Novembre at UCLA, who wanted to understand how the human genome varies on a continental scale. To that end, they looked at the genomes of over 1.300 people sampled from almost three dozen countries across Europe. The sample was originally collected by GlaxoSmithKline to hunt out genetic variations that influence the effectiveness of drugs and their side effects, but Novembre's team put it to use in understanding the links between genes and geography instead.
They analysed at single-letter differences in DNA ("single nucleotide polymorphisms" or SNPs) at about 200,000 places in each of the genomes. They compared this data to each person's country of origin as well as that of their grandparents if possible.
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The result was startling - the genetic and geopolitical maps of Europe overlap to a remarkable degree. On the two-dimensional genetic map, you can make out Italy's boot and the Iberian peninsula where Spain and Portugal sit. The Scandinavian countries appear in the right order and in the south-east, Cyprus sits distinctly off the "coast" of Greece.
Zoom in closer, and the map even reveals distinct genetic cluster within Switzerland based on the language people speak. German-speaking Swiss cluster to the east, Italian speakers to the south and Francophiles to the west. Even so, the clusters overlap and in general, the data reveals a genetic continuum between Europeans, where the borders of the genetic map are fuzzier than those of its geographical counterpart. As far as genes are concerned, the closer together two people live, the more similar their DNA is.
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The results have implications for a lot of biomedical research. Many scientists are scanning entire genomes on a hunt for SNPs that affect a person's risk of diseases like cancer or their reaction to drugs. Novembre says that researchers who are running these "whole-genome studies" need to bear in mind where their sample has come from. Even if a study looks at a small and seemingly related parts of Europe, it would have to adjust for any geographical influences in the genetic variations it uncovers.
Read it all here.