 It is possible that it is not actually the diffusion and gradient of Dpp that patterns tissues, but instead cells that receive Dpp signal instruct their neighbors on what to be, and those cells in turn signal their neighbors in a cascade through the tissue.Several experiments have been done to disprove this hypothesis and establish that it is actually the gradient of actual Dpp molecules that are responsible for patterning.Mutant forms of the Dpp receptor Tkv exist that behave as if they are receiving high amounts of Dpp signal even in the absence of Dpp.