Genetics of speciation in the Drosophila Willistoni complex

    Protein electrophoresis can be used to measure genetic differentiaion among natural populations. The Genetic Identity (I) at a locus is the probability that two alleles drawn from two different individuals are identical. These diagrams show the average genetic identity across many loci among individuals drawn from different populations, subspecies, sibling species, and non-sibling species. For example, in comparisons among  geographic populations, <1% of loci show fixed differences (bar at I = 0.0) and >90% of loci show no allelic differences (bar at I = 1.0). Among morphologically distinguishable subspecies, about 5% of loci show fixed allelic differences. More than 30% of loci in reproductively isolated sibling species are fixed. (modified from Ayala 1975)