Modeling Mitochondrial Population Genetics

Abstract

<p>Indirect tests have detected recombination in diverse animal mitochondrial DNA (mtDNA), including mammals. These results have far reaching implications for evolution and ecology, as virtually all animal population genetics studies assume mtDTA is clonally inherited. For the first time, we demonstrated that the molecular patterns detected by these tests could alternatively be explained by mutation rate heterogeneity, or clusters of sites with unusually low or high mutation rates. The false positive rates of six common tests for recombination were evaluated under models of mutation rate heterogeneity with theoretical and biologically estimated parameters. All tests produced an elevated level of false positives, casting serious doubts on the claim that animal mtDNA does not follow clonal inheritance.</p> <p>With uniparental inheritance, a haploid genome, multiple copies within a cell, and a replication cycle that is independent of the cell cycle, mitochondria population genetics are markedly non-Mendelian. Numerous questions remain in mitochondrial population genetics theory, such as the effect of dominance in the context of unique mitochondrial biology. Using simulations, we determined the fixation probabilities of advantageous mtDNA mutations under various modes of dominance and levels of polyploidy within a cell. The effect of a bottleneck and multiple cell lines (somatic and germ) with different selective pressures was investigated. The effect of increasing drift on fixation probabilities depends on the mode of dominance: recessive mutations become more likely to fix, but dominant mutatinos become less likely to fix. These results support the theory that drift plays a fundamental role in maintaining evolutionary stability of mitochondria by increasing the genetic variation among offspring, but suggests that the efficiency of this mechanism involves a more complex interaction between dominance and drift than previously thought.</p>