Stage 16 mmy^J1201 homozygous embryos have slightly fewer midline glial cells than wild-type (an average of 2.5/neuromere compared to a wild-type average of 3), and those present are misplaced. The longitudinal connectives are thinner and closer to the midline and segmental commissures are located closer together. There are severe fasciculation defects at the midline with many axons being much more loosely fasciculated than in wild-type. Fasciculation of axons is also much looser in the peripheral nervous system and chordotonal organ clusters are disorganised.

More than 90% of stage 16 mmy^J1201 embryos have a dorsal hole, this falls to about 50% in mutant larvae. These embryos and larvae also exhibit a weak general differentiation of the cuticle. During dorsal closure, leading edge cells are more rounded than in wild-type.

Eyes consisting mainly of mmy^J1201 homozygous somatic clone cells (generated using Scer\FLP1^ey.PN with Scer\FRT) are small with irregularly spaced ommatidia. In eye discs of this genotype, fewer photoreceptor cells differentiate posterior to the furrow and those that do form are irregularly spaced.