TYRO3 and retinal degeneration: Conclusive evidence that Tyro3 is necessary for the modifier effect came from examining Mertktm1Gkm/tm1Gkm; Tyro3129/B6 versus Mertktm1Gkm/tm1Gkm; Tyro3−/B6 offspring from a Mertktm1Gkm/tm1Gkm; Tyro3B6/B6 x Mertktm1Gkm/tm1Gkm; Tyro3−/129 cross, which demonstrated a more severe retinal degeneration phenotype in Mertktm1Gkm/tm1Gkm; Tyro3−/B6 mice.