Dominance at Adh locus in response of adult drosophila melanogaster to environmental alcohol

IT has been argued¹ that natural selection acting on enzyme polymorphisms may be most clearly demonstrated by challenging polymorphic populations with an environmental additive acting as a specific substrate for the enzyme under study. Wills and Nichols², for example, showed that, in their experimental conditions, heterozygote advantage at the octanol dehydrogenase locus in D. pseudoobscura depended on the presence of octanol in the food medium. Similarly, de Jong et al.³ found that the amylase^4,6 variant increased strikingly in frequency in populations of D. melanogaster moved from a sucrose to a starch-rich food medium. Amy ^4,6 is known to possess the highest in vitro activity on starch substrates of all common amylase variants⁴. We have examined the relationship between mortality and genotype at the alcohol dehydrogenase (Adh) locus when adult Drosophila are exposed to environmental ethanol.