A consortium（财团，联合） led by scientists at the University of Oxford and Harvard Medical School has constructed the world's most detailed genetic map. A genetic map specifies the precise areas in the genetic material of a sperm or egg where the DNA from the mother and father has been reshuffled in order to produce this single reproductive cell. The biological process whereby this reshuffling occurs is known as "recombination." While almost every genetic map built so far has been developed from people of European ancestry, this new map is the first constructed from African American recombination genomic data.

"This is the world's most accurate genetic map," said David Reich, professor of genetics at Harvard Medical School, who co-led the study with Simon Myers, a lecturer in the Department of Statistics at the University of Oxford.

The researchers were surprised to find that positions where recombination occurs in African Americans are significantly different from non-African populations.

"The landscape of recombination has shifted in African Americans compared with Europeans," said Anjali Hinch, first author and a post-graduate student at Oxford University's Wellcome Trust Centre for Human Genetics.

Simon Myers added, "More than half of African Americans carry a version of the biological machinery for recombination that is different than Europeans. As a result, African Americans experience recombination where it almost never occurs in Europeans."

The findings will be published in the July 21 edition of Nature.

An independent study that used a similar strategy to build a genetic map in African Americans—led by University of California, Los Angeles, scientists Daniel Wegmann, Nelson Freimer and John Novembre—will be published in Nature Genetics.

Scientists have only recently begun to explore the genetic differences between individuals and populations — and the role those differences play in human health. In that respect, the first draft of the human genome, completed a decade ago, was only a starting point for understanding the genetic origins of disease.

As researchers begin to parse（理解，解析） those differences, a crucial tool is a genetic map, which in this case was based on where recombination has occurred across the genome. Recombination, together with mutation, accounts for all the genetic (and thus physical) variety we see within species. But while mutation refers to the errors introduced into single locations within genomes when cells divide, recombination refers to the process by which huge chunks of chromosomes are stitched together during sexual reproduction.