The robo3³ allele is homo- and hemizygous viable.

Posterior R8 photoreceptor axons take an aberrant path to the proximal medulla in

robo3³ homozygous optic lobes

In general, no mutant phenotypes are observed for clones of robo3³ mutant cells scattered throughout the eye surrounded by heterozygous and homozygous wild-type cells. Mutant phenotypes are observed only when posterior R cells are rendered homozygous mutant. Homozygous robo3³ mutant posterior R cells extending into an otherwise wild-type optic lobe project aberrantly to the distal medulla. The mis-projecting robo3³ mutant posterior axons often disrupt the normal columnar organization of the medulla. However, the organisation of R8 axons projecting from more anterior regions of the eye disk is largely unaffected by homozygous robo3³ mutant cells.