As researchers begin to parse 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.
But this stitching process only occurs at specific locations. In a prior landmark set of papers, Myers and his colleagues identified a DNA code, or motif, that attracted part of the recombination machinery, a gene called PRDM9. Knowing the motif, a string of 13 DNA letters, researchers could zero in on the locations where recombination typically occurredthe "recombination hotspots."
"When recombination goes wrong, it can lead to mutations causing congenital diseases, for example diseases like Charcot-Marie-Tooth disease, or certain anemias," said Myers. "We found the same 13 base motif marking many of these disease mutation sites."
Explained Reich, "The places in the genome where there are recombination hotspots can thus also be disease hotspots. Charting recombination hotspots can thus identify places in the genome that have an especially high chance of causing disease."
The researchers discovered that the 13 base-pair motif that is responsible for many of the hotspots in Europeans accounts for only two thirds as much recombination in African Americans. They connected the remaining third to a new motif of 17 base pairs, which is recognized by a version of the recombinational machinery that occurs almost exclusive
|Contact: David Cameron|
Harvard Medical School