Half a million SNPs were decoded for each subject, but to get an overall assessment of the difference between any two genomes, the researchers used a mathematical trick that scrunched the hundreds of thousands of SNPs into two coordinates, with each person's genome represented by a point.
The greater the distance between two points, the greater the difference in their genomes.
A striking map of Europe emerged when the two teams plotted thousands of genomes on a single graph along with their country of origin.
While Spanish and Portuguese genomes clustered "south-west" of French genomes, Italian genomes jutted "south-east" of Swiss.
The researcher said that though the cardinal directions were artificial, the spatial relationships between genomes were not.
The closer together two people lived, they added, the more similar their DNA.
Telling about the accuracy of the map, Novembre revealed that when a geopolitical map was placed over it, half of the genomes landed within 310 kilometres of their country of origin, while 90 per cent fell within 700 km.
Both teams found that southern Europeans boast more overall genetic diversity than Scandinavians, British and Irish.
"That makes perfect sense with the major migration waves that went into Europe," says Kayser, noting Homo sapien's European debut 35,000 years ago, post-ice age expansions 20,000 years ago, and movements propelled by the advent of farming 10,000 years ago.
In each case, members of established southern populations struck north.
"A pattern in which genes mirror geography is essentially what you would expect from a history in which people moved slowly and mated mainly with their close neighbours," says Noah Rosenberg, a geneticist at the University of Michigan in Ann Arbor.
The studies have been published in the journals Nature and Current Biology.
Source-ANI
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