PDE6B and retinal degeneration: In addition, we found that both Em/J and CFW mice were homozygous for a nonsense mutation (p.Y347X) in exon-7 of the gene for phosphodiesterase 6 beta-subunit (Pde6b) on chromosome-5 (Supplementary Table 3) that underlies an autosomal recessive form of retinal (rod-photoreceptor) degeneration 1 (rd1, rodless)—consistent with prior reports that CFW mice undergo early-onset retinal degeneration, (Kuck et al. 1981; Serfilippi et al. 2004; Han et al. 2013).