Fig. 5. Rescue of roe. (A-D) Adult eyes and (E) quantification of photoreceptors. (A) Wild type. (B) rn¹⁶/rn²⁰ a roe null combination displays a small and rough eye. (C) UAS-roe can rescue roe. sev-GAL4/UAS-roe;rn¹⁶/rn²⁰ have larger and apparently less rough eyes than roe. (D) UAS-rn fails to rescue roe. sev-GAL4/UAS-rn;rn¹⁶/rn²⁰ eye shows no sign of rescue, instead an apparent enhancement of the roe phenotype. (E) Quantification of the rescue of roe mutants. Adult eyes were sectioned and the number of Elav-positive cells in each ommatidia was counted. Wild-type ommatidia carry the typical seven (R1-7) photoreceptors (the R8 photoreceptor cell body is located slightly offset and was not included). In roe mutants we find an average of 5.7 photoreceptors, which is rescued to 6.3 by providing roe activity using UAS-roe (P<0.04). Using UAS-rn we find no evidence of rescue and roe ommatidia contain an average of 5.6 photoreceptors per ommatidia. In addition we find ommatidia with 4 or sometimes only 3 photoreceptors, something not observed in the other genotypes, indicating a negative action of UAS-rn.