That is, the requirement to inactivate p107 or p130 in addition to Rb in the mouse would be expected to mask potential for the murine retinoblastoma cells to exhibit photoreceptor character, as there is widespread death of both rods and cones in the absence of Rb and p107 or Rb and p130 when deleted in early progenitors using Pax6 alpha Cre [67,68]. The gene discussed is RBL2; the disease is retinoblastoma.