Mutant flies exhibit a number of phenotypes. 10-20% of ommatidia lack a normal R7 and have in its place a photoreceptor cell, which contains a large rhabdomere that extends the depth of the retina. The presumptive R7 appears to develop as an outer photoreceptor. Ommatidial lenses of mutant eyes are severely disrupted. Supernumerary photoreceptors form on the R3/4 face of ommatidia, and ommatidial chirality is randomized or lost. When en::Su(H)^hs.2sev somatic clones are induced, a weakly penetrant transformation of presumptive R7s into outer photoreceptors is seen. In these cases, the cell in the R7 position is always mutant.

Eyes of flies carrying en::Su(H)^hs.2sev contain a high preponderance of symmetrical ommatidia. In mosaic ommatidia, in which only one cell of the R3/R4 pair carries en::Su(H)^hs.2sev, that cell invariably develops as an R3 photoreceptor, while the other cell develops as an R4 photoreceptor, resulting in incorrect chirality in some cases. The R8 cell body normally achieves an asymmetric position on the R3 rather than the R4 side of the ommatidium in wild-type flies. Frequent uncoupling of the R8 position from the R3/R4 asymmetry is seen in en::Su(H)^hs.2sev mosaics. In these cases, R8 cells are usually found between R5/R6, occasionally found between R1/R6 and in rare cases are found between other cells.