Interaction of non-allelic loci in expression of the extra-sexcomb phenotype inDrosophila melanogaster

Summary The expression of the extra-sexcomb phenotype is enhanced in males that are doubly heterozygous for mutants from two non-allelic loci,extra-sexcomb (Polycomb, Extra-sexcomb) andbithorax (bithorax, bithoraxoid, Ultrabithorax) as compared to the expression of the extra-sexcomb mutants when no bithorax mutants are present in the genotype. If the bithorax mutants are recessive, the expression is usually greater when the non-allelic mutants are cis-hererozygotes than when they are trans-heterozygotes, but there is no difference between cis-and trans-heterozygotes in extra-sexcomb andUltrabithorax compounds.This work, begun while the author was a member of the staff of the Zoology Dept. of the University of California at Berkeley, was completed, with the assistance of a National Institutes of Health research grant (RG-6754), in the Dept. of Genetics of the University of Turku.