Genetic control of Adh expression in Drosophila melanogaster.

Natural variants displaying different levels of expression of the gene for alcohol dehydrogenase (Adh) were subjected to genetic mapping experiments. The strains studied carry one of the two common electrophoretic forms of the enzyme. The difference among Adh-fast strains appears to be due to multiple loci with trans-acting effects. Differences among Adh-slow strains are due to modifiers or quantitative sites located very close to the structural gene (less than 0.05 map unit) or part of it. The modifiers detected in the Adhs strains seem to operate only on the structural allele in the cis-position.--A modifier that affects the ratio of ADH levels in larvae and adults was also detected in the Adhs strains. This modifier is also closely linked to Adh and is cis-acting.