The vestigial gene product is required for the completion of wing development in Drosophila melanogaster. In the absence of vestigial gene expression, cells within the larval wing and haltere imaginal discs fail to proliferate normally thus producing adults with severely reduced wings. Of a large number of vestigial mutations that have been characterized, only two are currently known to exist, vestigial(U) and vestigial(W), which manifest a significant dominant phenotype. Both are associated with chromosomal inversions that fuse the majority of the vestigial coding regions to other genes; mastermind in vestigial(U) and invected in vestigial(W) Examination of vestigial expression in the presence of these dominant alleles shows alterations in the disc-specific expression of vestigial during later stages of larval development. These patterning disruptions are specific to cells of the wing imaginal disc, as significant suppression of total levels of vestigial expression within entire larvae could not be detected. This dominant interference of vestigial patterning appears to be mediated in part by the vestigial coding sequences that are within the gene fusions. Further evidence that the dominant phenotype is the result of disrupted vestigial patterning comes from observations that the dominant alleles can be partially suppressed by mutations within the Drosophila-epidermal growth factor receptor gene. Mutagenesis of vestigial(U) and vestigial(W) produced a series of alleles with partially dominant phenotypes that restored various amounts of the adult wing. These phenotypes can be correlated with alterations in specific portions of the vestigial sequences associated with the dominant alleles. In the presence of these partially dominant alleles, wing imaginal discs have significantly more cells which express vestigial compared with the number associated with the original dominant phenotype. Additionally, eliminating some of the dominant effect causes alterations in the patterns of early stage apoptotic cell death associated with dominant vestigial alleles. Utilizing these new vestigial alleles, it is possible to correlate the consequence of altered vestigial expression to subsequent changes in patterning of the wing disc.