One of the most widely used markers in population genetics, mitochondrial genetic diversity, does not accurately reflect the size and history of a population, according to a report in this week's Science. This suggests natural selection may be acting on mitochondrial DNA (mtDNA), the authors note."This result opens questions -- what is mtDNA adapting to?" co-author Nicolas Galtier at the University of Montpellier in France told The Scientist.MtDNA is widely believed to be nearly evolutionary neutral. Therefore, mitochondrial genetic diversity should increase as a species' population size increases, and looking at mtDNA diversity should enable researchers to infer whether a species is advancing or declining.In the present study, the researchers assembled a database dedicated to sequence polymorphism by scanning GenBank and EMBL-Bank. To check its reliability, they compared the resulting information on the nuclear DNA of 417 species and the mtDNA of 1,683 species with allozyme data for...

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