Unequal crossing over occurs in females heterozygousw a /w a4 such that a deficiency and duplication can be recovered regularly. A triplication was also found following crossing over in the homozygous duplication. Genetic analysis of the duplication showed that of the several knownw loci only thew e andsp-w loci are duplicated. By means of crossing overw e andsp-w were introduced separately into the left half of the duplication andw e into the right half. The phenotypic consequences of such substitutions are interpreted in terms of the loci which are included in specific functional units or genes. They suggest thatw e andsp-w are in distinctive functional units. The fact that these duplications and deficiencies are without obvious affect on salivary gland band morphology suggests that the gene loci constitute only a small portion of the band structure.