The sev enhancer drives expression of a mutated Jra coding sequence in which a number of phosphorylation sites have been mutated to non-phosphorylatable residues: Ala replaces Ser or Thr at positions 58, 62, 73, 89, 91, 93 and 95.
Only a few ommatidia have lost one photoreceptor cell and some contain an additional outer photoreceptor. Loss of photoreceptor phenotype is enhanced by loss of a functional copy of Jra (Jra1 or JraIA109) and the presence of extra photoreceptors has disappeared.