Abstract
A regulatory mutant of the Adh (alcohol dehydrogenase) gene was induced by ethyl methanesulfonate. The mutation reduces the ability of the gene to complete for the limited gene activating factor. The mutant shows full activity in the homozygote but only one-half the activity of the progenitor gene in heterozygotes where it is competing with another allele for the limited factor. Evidence is presented for multiple regulatory sites in both the Adh and Adh2 loci.