Homozygous unc-104¹⁶⁰ mutant eyes externally appear normal and their ERGs show robust responses to light. However, the 'on-off transients' of ERG, which require synchronous synaptic transmission from the photoreceptors to second-order neurons, are absent in homozygous mutant eyes.

Homozygous unc-104¹⁶⁰ mutant flies die as unhatched late-stage embryos. The gross morphology of these embryos is comparable to that of a wild-type fly that has completed embryogenesis 20-22hrs after egg-laying. The mutants, however, are paralyzed and lack the coordinated muscle peristalsis required for hatching.

Homozygous unc-104¹⁶⁰ mutant embryos, despite normal axonal outgrowth and targeting, ISNb axon contacts lack extended branches. Filipodia-like structures are sometimes found, but not restricted to muscle boundaries. At 21 hours AEL, the nerve is visible in its target regions, but the contacts have not transformed into mature synapses; the nerves lack the bead-like boutons seen in wild-type embryos. Instead, the endings and their branches are more constricted than those at 14 hours AEL and frequently retain some filipodia-like processes. This phenotype is completely penetrant, observed in every abdominal segment. At times, axons at the boundary of muscles 12 and 13 are not found, raising the possiblity that some have retracted. Occasionally, ectopic projections from neighboring nerves are found. However, those that form in unc-104¹⁶⁰ mutants do not have boutons. Consequently, both the normal innervation and the occasionally ectopic projection are incapable of normal morphogenesis.