Fig. 2. R8 photoreceptors are frequently twinned in ed mutants. (A-E) Confocal microscopy for immunohistochemical detection of Ato (green) and Sens (red) (A,C,E), and Ato (green) and Boss (red) (B,D) in third larval instar eye discs. (A,B) Wild type. (C,D) ed^4.12/ed^4.12. (E) ed^lH23/Df(2L)ed-dp. A twinned R8 precursor pair is indicated by the arrow. (F) Expression of an R7 enhancer trap (R70-9) in an ed^4.12 mutant background. Immunohistochemical detection of Sens (red) and ß-galactosidase (green). The open arrow indicates a wild-type R8/7 pair. The closed arrow indicates twinned R8s with associated twinned R7s. The arrowhead indicates a twinned R8 with a single R7. Anterior is towards the left in all figures.