Figure 7. Schematic of periodic pattern formation neck and body skin.

A single core periodic patterning system based on a reaction-diffusion mechanism operates across the body and neck. Such a system operating in isolation has a single characteristic wavelength, thus producing placodes at a single density (right). Sensitization of neck skin to BMP signals as a result of RA production in this region alters the output of the patterning mechanism, allowing a reduction in feather density or the abolition of neck feathering, depending on the global level of BMP at the onset of patterning.