EUGENE– A study published in this week’s issue of Science magazine suggests that mutations occur in higher organisms about 100 times as often as scientists have previously believed.

The research described in the article provides the first direct estimate of mutation rates in a complex organism and "yielded a dramatic and unexpected result," according to one of the paper’s lead authors, University of Oregon biologist Michael Lynch.

Lynch and his fellow researchers are exploring mitochondrial DNA in a tiny roundworm (C. elegans). In the past decade, scientists have discovered a large number of human neuro-muscular disorders related to mutations in human mitochondrial DNA, a part of the human DNA sequence. Bio-medical advances regularly are achieved by crosschecking genetic sequences between species. Lynch’s work is funded by the National Institutes of Health.

"Our work indicates that the roundworm might be a very useful model species in discovering the genetic determinants of these human genetic diseases," says Lynch, who has studied mutations for 15 years. He is a member of the UO Department of Biology’s Ecology and Evolution Group.

For the study published in Science, members of Lynch’s laboratory raised 100 strains of the roundworm–all lines were genetically identical at the start of the study. Over a period of several years, the strains reproduced through approximately 200 generations. At that point, Lynch sent specimens to his collaborator, Dr. W. Kelley Thomas at the University of Missouri–Kansas City.

Thomas’ laboratory sequenced almost 1 million base pairs of worm DNA, a task only made possible in recent years due to breakthroughs in rapid sequencing technologies.

A count of the mutations revealed a mutation rate "approximately 100 times what the indirect estimates of mutation rate previously reported in textbooks would have led us to expect," Lynch notes.

He speculates that the mutation rate in human mitochondria is almost certainly higher than that found in roundworms. Humans have a higher metabolic rate, which leads to the production within the cell of additional metabolic byproducts known as free radicals.

"Free radicals are known mutagens and thus we humans might be candidates for an even higher mutation rate than the rate we found in the worm," says Lynch.

The increasing amount of mutagens in our environment is a potential threat to human health. In almost all species, mutations result in decreased viability and reduced fertility of the bearers, which in turn prevents mutations from accumulating in the species.

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