A statistical analysis of nucleotide substitutions in the Drosophila Adh region reflects irregularities in molecular clocks

Substitutions rates are expected to be rather constant when a gene is compa red between species. To analyze this feature, Ka/Ks ratios have been studie d for Alcohol dehydrogenase (Adh) and Alcohol dehydrogenase duplication (Ad h-dup) genes in Drosophila species. Adh Ka/Ks values are lower in intrasubg enus comparisons involving species of the Sophophora group than when these species are compared to the D. immigrans and S. lebanonensis, and this diff erence does not occur in the Adh-dup comparisons.