Abstract
A mutant Hadnl was induced in Drosophila melanogaster and found to be deficient in beta-hydroxy acid dehydrogenase. This mutation was utilized to study the genetics and physiological expression of Had+ . Had+ was mapped to the X chromosome at 54.4 and seems to be the structural gene for the enzyme. Enzyme activity in male and female flies indicates that the gene shows both dosage compensation independent from dose effect and differential activity during ontogeny. Electrophoretic mobility data indicate that the enzyme is a dimer which forms by random association of subunits. The fact that the mutant shows no detrimental effect implies that the enzyme is dispensable, at least under laboratory conditions. The biological and technical implications of this gene--enzyme system are discussed.
