The response of the antenna imaginal disc to ectopic Antennapedia gene expression was explored in a heat shock Antennapedia (hsAntp) transgenic strain and in strains doubly transgenic for hsAntp and downstream enhancer trap targets. The distal to proximal changes in morphological transformation in response to Antennapedia product at different developmental stages were correlated with changing expression patterns of transgene targets from antenna to leg-like patterns. Dose-response studies indicated changing thresholds of response to Antennapedia. At particular stages and doses of Antennapedia product, cell differentiation of leg bristles was uncoupled from transformation of the third antennal segment to tarsus. The results suggest that determination for bristle type does not depend on a prior determination decision for organ type. The results also provide an avenue for exploring the nature of "competence" at cellular and molecular levels.