On the utility of heteroplasmy in genotoxicity studies: An example from Chornobyl

We examine the utility of mtDNA heteroplasmy in assessing genetic damage due to environmental insult. Site heteroplasmy was quantified in a 400 bp portion of the cytochrome b gene in voles from a contaminated area near Chornobyl, Ukraine and from a relative control site by examining pregnant females and their embryos. A four hundred base pair segment was sequenced from approximately ten clones from each mother and embryo. Taq and/or cloning mutations were evaluated to estimate technical error. Although the rates of substitutions in clonal variants for experimentals, biological controls and technical controls were 1 in 1,840 bp, 1 in 2,280 bp, and 1 in 3,333 bp, respectively, we could not reject the null hypothesis that the variants were the result of a single, combined, mutation rate. However, multiple substitutions and transversions were restricted to clones from the Chornobyl samples. Bootstrap analyses indicate that these aspects of variation were significantly different from the controls. Examination of the mitochondrial genome by cloning individual molecules for site heteroplasmy to estimate effects of pollution on mutation rate in free-living organisms appears to warrant additional study.