In order to confirm these microarray results, an in situ hybridization analysis of the putative up-regulated cone genes was carried out in which the rd7 mutant retina was compared with age-matched, wild-type controls. We found that the majority of the cone-specific genes that were up-regulated in microarray experiments were derepressed when assessed by in situ hybridization (Figure 2). There were two major patterns of cone gene derepression. The more common pattern (type I) manifested itself as ectopic gene expression throughout the ONL, consistent with gene expression in all photoreceptors (Figure 2; upper left photomicrographs). Typical examples of this pattern of derepression are shown in Figure 2, and many more are available in Table S1. This pattern of expression contrasts sharply with the usual pattern of cone gene expression, which consists of scattered cells localized to the scleral edge of the ONL (Figure 2).