Lethal in gynandromorphs. Bristles of the wing margin are small and unpigmented in clones. Clones in the wing blade are extremely elongated. Whereas control clones are 5-10 times longer than wide, with irregular borders, clones of cells monozygous for l(1)Mb281 are 30-50 times longer than wide, with smooth borders. This phenotype is found only in clones induced more than 48 hours before puparium formation.