MUTATIONS in the DNA of voles found in the 鈥渉ot zone鈥� around the devastated Chernobyl nuclear plant are cropping up at a far higher rate than expected. Results of research on the voles, presented at the annual meeting of the Society for the Study of Evolution in Montreal last month, raises questions about the full effect of radiation on animal populations and on humans.
American researchers led by Ron Chesser of the University of Georgia鈥檚 Savannah River Ecology Laboratory examined the DNA in mitochondria, the energy-producing bodies in the cell cytoplasm. They found 46 mutations in just one gene, the cytochrome b gene, in nine voles taken from the 30-kilometre restricted zone around Chernobyl. When they examined 10 animals from outside the 鈥渉ot zone鈥�, they found four mutations.
Chesser says he was surprised by the sheer number of mutations. There are 鈥渕any more mistakes than what was thought to be feasible in a thriving population鈥�, he says. The study raises questions for geneticists about how many mutations a population can tolerate without dying off, he says.
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The results also have implications for humans. The Atomic Bomb Casualty Commission spent years looking for any kind of genetic damage in the survivors of the Hiroshima and Nagasaki bombs, says Christopher Wills, an evolutionary geneticist at the University of California in San Diego. They did not report much beyond stillbirths and some cases of cancer, he says. James Crow, a member of the commission鈥檚 advisory committee says he has no doubt that genetic changes were induced by the radiation from the bomb 鈥渂ut they were below the threshold of detection鈥�. The new data may help researchers to home in on changes in people exposed to radiation at Chernobyl.
Researchers cannot agree on the natural background rate at which mutations appear in mitochondrial DNA. But even choosing a conservative rate 鈥� of, say, 1 in 100 000 per gene per generation 鈥� the voles from the contaminated zone have a mutation rate about 40 times that of the background rate, says Chesser. The rate was found to be high enough to cause mutations from one generation to the next.
The team is looking at other genes in mitochondria and in the nucleus to see if the effects are widespread. It would be strange, says Chesser, 鈥渇or us to have stumbled upon the only gene showing this kind of alteration鈥�.