Are entrenched characters developmentally constrained? Creating biramous limbs in an insect

Are evolutionarily entrenched phenotypes highly constrained developmentally? We explored this question in the case of the uniramous appendages of fruit flies. We created bi- and polyramous antenna/leg combinations in four different genotypes. Each genotype consisted of two relevant mutations. We suggest that not all entrenched characters are strongly constrained by developmental processes and that there exists sufficient natural genetic variation to alter highly conserved phenotypes.