Models of pattern formation during development. Alan Turing's model of pattern formation arising from the interaction of two morphogens is shown in (A). Red arrows indicate degradation, green arrow indicate autocatalysis. A key aspect of this model is that morphogens X and Y have different diffusion characteristics. (B), An example of a Turing pattern that was generated by a computer simulation of the model summarized in (A). Turing patterns in nature have been identified on squirrels, leopards, zebrafish and in the stripes of the marine angelfish pomacanthus, among others [27, 28]. (C), The coloration of this scribbled rabbit fish resembles computer simulated Turing patterns as well as Turing patterns observed on other marine fish. (D), The Gier-Meinhardt model of pattern formation. Autoactivation is coupled to production of an inhibitor of longer range. As a result, a homogenous distribution of activator is unstable resulting in a gradient of activator.