For example, there are genetic mutations within some mouse strains that can cause retinal degenerations such as the rd8 mutation in Crumbs homolog 1 (Crb1)199 and rd1 mutation in phosphodiesterase 6B (Pde6b).200,201 Before beginning any study, researchers should screen their mice to confirm the absence of these mutations in their colonies. Here, CRB1 is linked to retinal degeneration.