Tandem duplications in animal mitochondrial DNAs: variation in incidence and gene content among lizards

Size, location, gene content, and incidence were determined for 10 lizard mitochondrial DNA duplications. These range from 0.8 to 8.0 kilobases (kb) and account for essentially all of the observed size variation (17-25 kb). Cleavage-site mapping and transfer-hybridization experiments indicate that each duplication is tandem and direct, includes at least one protein or rRNA gene, and is adjacent to or includes the D loop-containing control region. Duplication boundaries are nonrandomly distributed, and most appear to align with tRNA genes, suggesting that these may play a role in the duplication process. Duplications are infrequent and usually restricted to particular individuals or populations. They appear to be ephemeral; in no case is the same duplication shared by mitochondrial DNAs from closely related species. Mitochondrial DNA duplications occur significantly more often in triploid than diploid lizards and at similar frequencies in hybrids and nonhybrids.