MOLECULAR CHARACTERIZATION AND EVOLUTION OF A DUCK MITOCHONDRIAL GENOME

We sequenced 6,478 bp of mitochondrial DNA from Peking duck (Anas plat yrhyncos). Eight protein genes, 11 tRNAs, part of the small and large ribosomal subunits, and the control region sequences were compared to homologous chicken sequences. The gene organization in duck and chicke n is identical but differs from other vertebrates in the juxtaposition of the tRNA(Glu)-ND6 genes next to the control region and in the lack of a hairpinlike structure between the genes for tRNA(Asn) and tRNA(C ys) used for light-strand replication. Protein, tRNA, and rRNA genes e volved mainly through base substitutions and small insertions and dele tions. Transitions greatly outnumber transversions in the tRNA and rRN A genes, but this bias is not evident in protein genes; the control re gion has a higher proportion of transversions. The duck and chicken co ntrol regions show a high frequency of length mutations. Large A-T-ric h nucleotide stretches dispersed across the region between the bidirec tional transcription promoter and the heavy-strand replication origin in the chicken are absent in the duck. Sequence elements for heavy-str and replication in mammals are conserved in the duck and chicken contr ol regions. Estimates of divergence for ribosomal RNAs and proteins ba sed on total substitutions, transversions, and amino acid replacements show that all the duck/chicken values are lower than the correspondin g mammal/mammal (cow, human, mouse) values. If paleontological data su ggesting that avian and eutherian ordinal radiation occurred at approx imately the same time are correct, this suggests that at great evoluti onary distance, rate of mitochondrial DNA evolution in birds is somewh at decelerated compared to mammals.