Numerical simulation of labelling in the 2D model. The top row shows anterograde "labeling spots" in retina. The following three rows display corresponding distribution of label in SC. The size of both retinal and collicular arrays is 100 by 100 cells. The three rows show results for wild-type, heterozygous knock-ins, and homozygous knock-ins, as marked on the left. Notice the doubling transition, when going from temporal to nasal injection in heterozygotes. This Figure is to be compared to Figure 4 from Ref. . α = β = 30. The color map is shifted in each image for visibility. Abbreviations: D, dorsal; V, ventral; N, nasal; T, temporal; C, caudal; R, rostral; L, lateral; M, medial.