SEQUENCE EVOLUTION IN AND AROUND THE MITOCHONDRIAL CONTROL REGION IN BIRDS

By cloning and sequencing 3.4 kilobases of snow goose mtDNA we found t hat the ND5 gene is followed by the genes for cytochrome b, tRNA(Thr), tRNA(Pro), ND6, tRNA(Glu), the control region, tRNA(Phe), and srRNA. This order is identical to that of chicken, quail, and duck mtDNA but differs from that of mammals and a frog (Xenopus). The mean extent of difference due to base substitution between goose and chicken is gener ally closer to the same comparison between rat and mouse but less than that between human and cow. For one of the nine regions compared (tRN A(Glu)), the bird differences appear to be anomalous, possibly implica ting altered functional constraints. Within the control region, severa l short sequences common to mammals are also conserved in the birds. C omparison of the goose control region with that of quail and chicken s uggests that a sequence element with similarity to CSB-1 duplicated on ce prior to the divergence of goose and chicken and again on the linea ge leading to chicken. Between goose (or duck) and chicken there are f our times more transversions at the third positions of fourfold-degene rate codons in mitochondrial than in nuclear genes.