The complete nucleotide sequence of the mitochondrial DNA of the fin whale, Balaenoptera physalus.

The composition of the mitochondrial DNA (mtDNA) of the fin whale, Balaenoptera physalus, was determined. The length of the molecule is 16,398 bp, and its organization conforms with that of other mammals. The general similarity between the mtDNA of the fin whale and the cow is greater than the similarity between the fin whale and other species (human, mouse, rat) in which the composition of the entire molecule has been described. The D-loop region of the mtDNA of the fin whale is 81% identical to the D-loop of dolphin DNA, and the central portion of the D-loop is similar to the bovine D-loop. The accumulation of transversions and gaps in the 12S and 16S rRNA genes was assessed by comparing the fin whale, cow, and human. The sequence difference between human and the whale and human and the cow was at the same level, indicating that the rate of evolution of the mtDNA rRNA genes is about the same in artiodactyls and cetaceans. In the 12S rRNA gene an accumulation rate of 0.05% per million years places the separation of cetaceans and artiodactyls at about 55 million years ago. The corresponding figure for human and either the whale or the cow is about 80 million years. In the 16S rRNA gene a 0.08% accumulation rate of transversions and gaps per million years yields concurring figures. A comparison between the cytochrome b gene of the fin whale and cytochrome b sequences in the literature, including dolphin (Stenella) sequences, identified the cetaceans as monophyletic and the artiodactyls as their closest relatives. The comparison between the cytochrome b sequences of the fin whale and Stenella showed that differences in codon positions one or two were frequently associated with a change in another codon position.