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Submitted by rhallice on Thu, 11/23/2017 - 22:19

The famous Englishman Alan Turin played a crucial role in decoding messages by the German Enigma machine during the Second World War, helping allied forces win the war. In 1952 he published the famous book on mathematical biology called The Chemical Bases of Morphogenesis developing his Turing-type reaction-diffusion system. For years scientist had believed that digit formation was controlled by a morphogen gradient of Sonic Hedgehog (Shh). A morphogen gradient is a developmental biological concept where the emission of a signal from a part of an embryo can determine the location, differentiation, and fate of the surrounding cells through the morphogen’s concentration. It was thought that the Shh morphogen controlled digit formation and that GLI3 transcription factor controlled the expression of Shh. However, researchers found the GLI3 and Shh mutants had displayed identical phenotypes of polydactyl limbs, or hands with more fingers. This in turn shows that digits can form in the absence of Shh. This is not a consistent observation that would support a morphogen gradient model. This shows that digits can form independent of Shh meaning that Shh gradient can pattern digit identity but is not a factor in determining where a digit occurs. However, this supports a Turing-type model in digit pattern where an interaction of activators and inhibitors plays a role in the wavelength and patterning of digits. A Turing-type reaction-diffusion mechanism involves an activator that also turns on its on inhibitor as well where the activator diffuses in a short distance and the inhibitor can diffuse further producing a repeating pattern. This repeating pattern resembles a wavelength of peaks over a distance.