Concerted evolution of sequence repeats in Drosophila mitochondrial DNA

In the eight Drosophila species of the melanogaster subgroup, the mitochondrial DNA (mtDNA) contains an A+T-rich region in which replication originates. Comparative study of the genomes found in the species with long mtDNA molecules reveals relative homogeneity of the repeat units within a given genome, which contrasts with the variability found among the repeats of different genomes. This result is suggestive of a process of a concerted evolution. The examination of heteroplasmic flies of three species (D. simulans, D. mauritiana , and D. sechellia ) has shed light on this process. The authors have analyzed an exceptional isofemale line in which three molecular lengths of mtDNA are found (molecules with four, five, and six repeats, respectively). Individual offspring of this line carry from one to three of the molecular types, in all combinations.