Their study, published in the April 11 issue of Nature, also shows that these mutations are caused mainly by random errors that occur during cell divisions rather than by environmental factors.
"Mutation is the ultimate source of variation," says Wen-Hsiung Li, Ph.D., the George Wells Beadle Distinguished Service Professor in the department of ecology and evolution at the University of Chicago. "Your ancestors and my ancestors accumulated different mutations, which is part of the reason why you and I look different."
For more than half a century, scientists have believed the main source of new mutations is in the male germ line. But two recent studies one from the Whitehead Institute (2000) and the other from the International Human Genome Sequence Consortium (2001) suggest the male-female ratio of mutation rate or alpha is only about 2-to-1, a drastic decrease from earlier estimates. Li and co-investigator Kateryna Makova, Ph.D., research associate in the department of ecology and evolution, have restored the validity of a high alpha among humans and apes.
Li and Makova studied part of the DAZ locus, a non-coding genetic sequence present on chromosome 3 and the Y chromosome. The researchers found a low male-female mutation rate when they compared closely related species, which involved a shorter evolutionary time span. For example, when they looked at humans, pygmy chimpanzees and gorillas, they found that alpha is only 1.4, which suggests there is only a slightly higher mutation rate in males than in females.
But for distantly related species, which, according to Li, better represent the general tre
Contact: Catherine Gianaro
University of Chicago Medical Center