Figure 4: (A) Schematic representation of the network of a general activator-inhibitor Turing model. The four reaction kinetic parameters are shown: fu, fv, gu, and gv. Fgf promotes a PD-graded distribution of the parameter fu to drive stripe orientation (gray dashed arrow). Hox and Fgf inhibit the parameter gu to increase the wavelength in a PD-graded manner (bold line). U, activator; V, inhibitor. (B) Graphs of the average digit period of the triple mutants with Gli3−/− background at four equidistant positions along the PD axis of the digital region. With the exception of Hoxa13+/–;HoxdDel11-13/Del11-13;Gli3XtJ/XtJ, a clear trend is observed: The PD gradient of wavelength is generally shallower as distal Hox genes are removed. (C) Graphs of average digit period (wavelength) versus distal Hox gene dose in the three different Gli3 backgrounds. A smooth positive correlation between Hox gene dose and wavelength is observed in all three cases. Figure and legend from Sheth et al. 2012.