Mitochondrial genome organization and vertebrate phylogenetics

With the advent of DNA sequencing techniques the organization of the verteb rate mitochondrial genome shows variation between higher taxonomic levels. The most conserved gene order is found in placental mammals, turtles, fishe s, some lizards and Xenopus. Birds, other species of lizards, crocodilians, marsupial mammals, snakes, tuatara, lamprey, and some other amphibians and one species of fish have gene orders that are less conserved. The most pro bable mechanism for new gene rearrangements seems to be tandem duplication and multiple deletion events, always associated with tRNA sequences. Some n ew rearrangements seem to be typical of monophyletic groups and the use of data from these groups may be useful for answering phylogenetic questions i nvolving vertebrate higher taxonomic levels. Other features such as the sec ondary structure of tRNA, and the start and stop codons of protein-coding g enes may also be useful in comparisons of vertebrate mitochondrial genomes.