FIGURE 1.

The arms race and co-evolution between selfish mitochondrial DNA and the host cell. Selfish mtDNA with a higher proliferation rate will gradually outcompete wild-type mtDNA in a sexual population. If the selfish mtDNA possesses harmful effects or carries other deleterious mutations, host fitness will be compromised after the selfish mtDNA reaches a certain frequency. When the selfish mtDNA is spreading through the population, the population starts to accumulate other mutations to restore the host fitness. Strong restoring mutations may occur in the nuclear genome that directly offset the harmful effect of the selfish mtDNA. Alternatively, weak restoring mutations may occur in both mitochondrial and nuclear genomes to compensate for the effect of deleterious mutations. In both scenarios, the evolved mitochondrial and nuclear genomes are different from the ancestral ones, but the host fitness remains the same.