fu1 heterozygotes carrying one copy of Su(fu)+ display a partially suppressed wing phenotype, the presence of P{SUFU200} produces viable males with a fu1 wing phenotype (the transposon fully compensates the decreased amount of Su(fu)+ product). fu41 heterozygotes carrying one copy of Su(fu)+ are pharate adult lethal and display a cos wing phenotype, the presence of P{SUFU100} produces viable males with a fu41 wing phenotype (the transposon fully compensates the decreased amount of Su(fu)+ product).