Interspecific Gene Differences and Evolutionary Time Estimated from Electrophoretic Data on Protein Identity

A statistical method is developed for estimating the number of gene differences and evolutionary time of a pair of species from electrophoretic data on protein identity. This method is applied to the Drosophila data available. It is shown that the evolutionary time for a pair of nonsibling species in Drosophila is on the average three times longer than that for a pair of sibling species. It is also shown, under certain assumptions, that pairs of recent sibling species differ in about one to two amino acids per protein, and it is estimated that 500,000 years were required to establish such a difference.