Do mitochondria recombine in humans?

Until very recently, mitochondria were thought to be clonally inherited thr ough the maternal line in most higher animals. However, three papers publis hed in 2000 claimed population-genetic evidence of recombination in human m itochondrial DNA. Here I review the current state of the debate. I review t he evidence for the two main pathways by which recombination might occur: t hrough paternal leakage and via a mitochondrial DNA sequence in the nuclear genome. There is no strong evidence for either pathway, although paternal leakage seems a definite possibility. However, the population-genetic evide nce, although not conclusive, is strongly suggestive of recombination in mi tochondrial DNA. The implications of non-clonality for our understanding of human and mitochondrial evolution are discussed.