Human mitochondrial DNA recombination: can it be true?

Abstract

Pity the evolutionary geneticists trying to keep track of mitochondrial DNA (mtDNA) inheritance. Sure there are rules of thumb, but none has ever been so sturdy or so widely applicable as Mendel’s Laws are for eukaryote nuclear genes. Plants exhibit the panoply of mtDNA inheritance, with some showing strictly sex-limited transmission (either paternal or maternal) and a few showing biparental inheritance1. For other anisogamous organisms, the working model has usually been one of strictly maternal inheritance, although now that we have well confirmed, striking exceptions in mussels2,3, as well as occasional reports of paternal leakage in other organisms4–6, one might never feel too sure. The most recent affront to simplicity is the claim that a human’s mtDNA is sometimes a mixture of conventional maternal mtDNA that has recombined with mtDNA from somewhere else7–9. The claims are disconcerting because so many researchers study human mtDNA, and do so while relying upon the assumption that nonmaternal inheritance and recombination do not occur.