Photoreceptor precursor cells are post-mitotic precursor cells which can differentiate into cones or rods, which eventually express different photopigments (M opsin or S opsin in cones, and rhodopsin in rods). In humans, all photoreceptors are prenatally generated. However, in the mouse, cones are formed in the embryonic stage, while rods are formed both prenatally and postnatally. Late photoreceptor precursor cells give rise to the rod photoreceptors.