First, close evaluation of the staining pattern of a number of type I genes in the rd7 mutant retina (e.g., see Table S1, genes G9, G19, and G24), reveals that, in addition to the background staining throughout the ONL, there is a more darkly staining subpopulation of cells scattered throughout this layer in a distribution corresponding to that of the supernumerary S-cone opsin-expressing cells.