"The key is to uncover the ancestry of each segment of the genome," Novembre said. "Switch points enable us to identify recombination 'hot spots,' where recombination rates are high."
Explaining recombination, Novembre said, "When we pass on DNA to our children, we stitch together the DNA we received from our mother and father. The resulting DNA alternates between DNA from your mother and from your father, and the recombination points are the boundaries. Those points could be chosen uniformly across the whole chromosome, but studies have found that recombinations occur in some locations in the chromosome more than in others. Locations in the chromosome have particular recombination rates the rate at which break points occur in that location.
"It is difficult to identify, by studying chromosomes directly, where the stitch points are between maternal and paternal DNA," he said. "In individuals of mixed ancestry, however, such as African Americans and African Caribbeans, we can identify switch points between African ancestry and European ancestry. These switch points mark locations where recombinations have occurred at some point in the past."
"There are regions of our map that differ from what we would expect," Wegmann said. "We see locations where there are deficiencies in recombination, and they line up with the locations of mutations that rearrange the genome and flip a piece of DNA to invert it. When you have a normal copy of the DNA and an inverted copy of the DNA, one from your mother and one from your father, this inversion suppresses recombination."
Of some 3 billion base pairs in a person's genome, the scientists were able to resolve recombination rates down to 50,000 base pairs of the DNA an impressive figure.
Comparing this African American recombination map with that of other populations enables researchers to locate recombination hot spots, which have hi
|Contact: Stuart Wolpert|
University of California - Los Angeles