As the human genome gradually yields up its secrets, scientists are finding some genetic events, such as rearrangements in chromosomes, are less random than they had previously thought. Originating as structural weaknesses in unstable stretches of DNA, abnormal chromosomes may, rarely, result in a disabling genetic disease one or two generations later. A report in the Feb. 17 issue of Science by genetics researchers at The Children's Hospital of Philadelphia and the University of Pennsylvania analyzes genetic predisposition to the translocation t(11;22), a swapping of genetic material between chromosomes 11 and 22. They found an unexpectedly high frequency of new...
