Three of the strains (CAST/EiJ, AKR/J, NOD.NON-H2-nb1) are known to harbor suppressor alleles for retinal degeneration associated with the rd7 phenotype [6] while one strain, C57BL6/J (B6), exhibits 100% penetrance for the disease. This evidence concerns the gene NR2E3 and retinal degeneration.