Calibration of mitochondrial DNA evolution in geese.

Mitochondrial DNA was purified from five American species of geese representing the genera Anser and Branta, which have fossil records. The results of electrophoretic comparisons of about 75 fragments per individual produced by 14 restriction enzymes imply that the mean extent of sequence divergence between species of Anser and Branta is about 9%. Fossil evidence suggests that these two groups of geese had a common ancestor 4-5 million years ago. Thus, the mean rate of sequence divergence in goose mitochondrial DNA is not far from 2% per million years, the value in mammals.