Animal mitochondrial genomes

Animal mitochondrial DNA is a small, extrachromosomal genome, typically sim ilar to 16 kb in size. With few exceptions, all animal mitochondrial genome s contain the same 37 genes: two for rRNAs, 13 for proteins and 22 for tRNA s, The products of these genes, along with RNAs and proteins imported from the cytoplasm, endow mitochondria with their own systems for DNA replicatio n, transcription, mRNA processing and translation of proteins. The study of these genomes as they function in mitochondrial systems-'mitochondrial gen omics'-serves as a model for genome evolution. Furthermore, the comparison of animal mitochondrial gene arrangements has become a very powerful means for inferring ancient evolutionary relationships, since rearrangements appe ar to be unique, generally rare events that are unlikely to arise independe ntly in separate evolutionary lineages. Complete mitochondrial gene arrange ments have been published for 58 chordate species and 29 non-chordate speci es, and partial arrangements for hundreds of other taxa, This review compar es and summarizes these gene arrangements and points out some of the questi ons that may be addressed by comparing mitochondrial systems.