nrm⁴⁸/nrm¹⁶⁵ transheterozygotes are viable, although the adults produced often have abnormal wing postures. A significant fraction of mutant embryos have central nervous system defects in abdominal segments A4 and A5. The MP1 pathway fuses with other lateral pathways and contacts the contralateral fascicles at the level of segments A4 and A5. Defects in the peripheral nervous system are also seen in abdominal segments A4 and A5. Approximately 35% of embryos either lack or show defective formation of a subset of muscles, primarily in abdominal segments A4 and A5.