Systematic and evolutionary studies in mammals: the contribution of the mitochondrial genome

Molecular data represent an important source of information for systematic and evolutionary studies; ideally this information should be evaluated toge ther with data coming from other approaches (e.g., paleontological and morp hological), since the molecular approach is limited by the availability of suitable homologous sequences, and these may be taxonomically informative o nly if they derive from speciation events (i.e., orthologous) and not from gene duplications (i.e., paralogous). This study focuses on the availabilit y of sequences from the vertebrate class of Mammalia. The results show a st rong bias in databases as, for some orders, little or no sequences are stor ed. For nuclear genes it is often difficult to discriminate between ortholo gous and paralogous ones. Therefore we advise the use in comparative studie s of entire mitochondrial genomes which are easy to sequence and only conta in orthologous genes. We report here the genetic organization of the mitoch ondrial DNA in mammals. In addition a phylogenetic tree of mammals, obtaine d by using the complete mitochondrial genomes of 23 species, is reported he re.