Genetic analysis of the sexual dimorphism of glass inDrosophila melanogaster

Abstract

SUMMARY: A modifier locus is described that alters the level of phenotypic expression of the third chromosome mutant glass in a sex specific manner. Alternative alleles either confer a sexually dimorphic level of pigment in glass mutants, with the male being greater, or cause similar expression in the two sexes. The alleles are indistinguishable in females but produce the respective phenotypes in males. The gene maps to the tip of theXchromosome at position 0·96 ± 0·11. Cytologically, the locus is present between polytene bands 3A6–8 and 3C2–3 as determined by its inclusion in translocatedXsegments inw+Y,Dp(l;2)w^70h31andDp(l;3)w^67k27The dimorphic allele is dominant to the nondimorphic condition in males heterozygous for an insertional translocation carrying the dimorphic allele and a normal chromosome carrying the nondimorphic form. The dimorphic allele in two doses in males does not exhibit a dosage effect. The modifier phenotype is unaffected in twoXflies by the presence of the transformer mutation.