Abstract
Drosophila melanogaster normally have six thoracic legs and no abdominal legs. However, one or two legs often appear in the first abdominal segment ofbithoraxoid mutants. The extent to which these extra legs develop is determined both by thecis-regulatory action ofbithoraxoid lesions onUltrabithorax and by the number of copies of the adjacent homeotic geneabdominal-A. Thebithoraxoid region does notcis-regulateabdominal-A.
