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 together with data coming from other approaches (e.g., paleontological and morphological), since the molecular approach is limited by the availability of suitable homologous sequences, and these may be taxonomically informative only if they derive from speciation events (i.e., orthologous) and not from gene duplications (i.e., paralogous). This study focuses on the availability of sequences from the vertebrate class of Mammalia. The results show a strong bias in databases as, for some orders, little or no sequences are stored. For nuclear genes it is often difficult to discriminate between orthologous and paralogous ones. Therefore we advise the use in comparative studies of entire mitochondrial genomes which are easy to sequence and only contain orthologous genes. We report here the genetic organization of the mitochondrial DNA in mammals. In addition a phylogenetic tree of mammals, obtained by using the complete mitochondrial genomes of 23 species, is reported here.