The Genetics of a Small Autosomal Region of Drosophzla Melanogaster Containing the Structural Gene for Alcohol Dehydrogenase. Affecting the Expression of Hairless 111. Hypomorphic and Hypermorphic Mutations

A lethal locus (1(2)br7;35B6-10), near Adh on chromosome arm 2L of D. melanogaster, is identified with Plunkett’s dominant suppressor of Hairless ( H ) . Of eight new alleles, seven act as dominant suppressors of H , the eighth is a dominant enhancer of H. One of the suppressor alleles is both a leaky lethal and a weak suppressor of H . Confirming NASH (1970), deletions of 1(2)br7 are dominant suppressors, and duplications are dominant enhancers of H . A simple model is proposed to account for the interaction of 1(2)br7 and H , assuming that amorphic (or hypomorphic) alleles of E(2)br7 suppress H and that hypermorphic alleles enhance H . p u s and allele specific suppressor and enhancer mutations are well known in Drosophila melanogaster, although there is little evidence for any particular example of the molecular basis of the specific interaction between suppressor (or enhancer) and suppressed (or enhanced) alleles ( see KAUFMAN, TASAKA and SUZUKI (1973) for review). NASH (1970) described the dominant suppression of the phenotype of Hairless by a deficiency of chromosome arm 2L that included a previously identified dominant suppressor of Hairless ( S u ( H ) ) . In the same paper NASH also gave evidence that duplications for the same chromosome region act as dominant enhancers of the Hairless phenotype. In this paper I present a further analysis of the suppression and enhancement of Hairless by Su(H) and its alleles and show that a lethal allele of Su(H) can act as a dominant enhancer of Hairless. MATERIALS A N D METHODS Four alleles of the third chromosome dominant mutation Hairless were used in this study. Both H i and HZ are old alleles and were included by PLUNKETT (1926) in his classic study of Hairless. Both are of spontaneous origin. The H I allele was on a third chromosome marked with both GI and Sb or GI alone. H57 is associated with Tp(3)H57 (VAN BREUGEL, RAY and GLOOR 1968), which has the new gene order: 61-86F7-11/97D1.2-95Cl.2/98C5-97D1.2/86F7.1195C1.2/98C5-100. Since H is not included within the deficiency segregant of T(1;3)05 (i.e., Df (3R)88C;92CD) and since H maps proximal to ebony (BRIDGES and MORGAN 1923), which is Genetics 101 : 447-459 July/August, 1’382.