Consistent with Tyro3 as a modifier gene, the retinal degeneration phenotype was more severe when Mertktm1Gkm/tm1Gkm was crossed with Tyro3−/− (targeted knockout) mice to generate Mertktm1Gkm/tm1Gkm; Tyro3−/− than in Mertktm1Gkm/tm1Gkm; Tyro3129/129 mice. The gene discussed is TYRO3; the disease is retinal degeneration.