A. In wild type, photoreceptor neurons (ELAV, magenta) differentiate clustered around central R8 cells (SENSELESS, green). Arrowhead indicates column 0 within the morphogenetic furrow, where single R8 cells are first individually resolved. Anterior to the left. B. In GMR-p21, photoreceptor differentiation is first observed in column 2, as in wild type (compare panel A). C. In wild type, cone cells (CUT, magenta) are first detected around ommatidia in column 10. D. Cone cells are detected no earlier in GMR-p21, despite not having to divide before differentiating.