What do patterns of genetic variability reveal about mitochondrial recombination?

Recent claims that patterns of genetic variability in human mitochondria show evidence for recombination, have provoked considerable argument and much correspondence concerning the quality of the data, the nature of the analyses, and the biological realism of mitochondrial recombination. While the majority of evidence now points towards a lack of effective recombination, at least in humans, the debate has highlighted how difficult the detection of recombination can be in genomes with unusual mutation processes and complex demographic histories. A major difficulty is the lack of consensus about how to measure linkage disequilibrium. I show that measures differ in the way they treat data that are uninformative about recombination, and that when just those pairwise comparisons that are informative about recombination are used, there is agreement between different statistics. In this light, the significant negative correlation between linkage disequilibrium and distance, in at least some of the data sets, is a real pattern that requires explanation. I discuss whether plausible mutational and selective processes can give rise to such a pattern.