Dissecting the evolutionary role of the gene in mouthpart diversification by full locus replacement.

genes determine positional codes along the head-to-tail axis. Here, we replaced the entire () locus, which controls the development of the proboscis and maxillary palps, with that from , a related species with highly modified mouthparts. The replacement rescues most aspects of adult proboscis morphology; however, the shape and orientation of maxillary palps were modified, resembling and closely related species. Expressing the Pb protein in the pattern fully rescued morphology. However, the expression pattern directed by cis-regulatory sequences differed from that of in cells that produce altered maxillary structures, indicating that regulatory sequences can evolve in related species to alter morphology.