Third instar larvae bearing one copy of Dscam1^+t73.3 show significant impaired locomotion in crawling and self-righting assays, as compared to controls. Neurotransmission at their neuromuscular junction shows significant increases in the amplitude and interval of miniature excitatory junction potentials (mEJP), a significant decrease in the amplitude of evoked excitatory junction potential (EJP) upon high frequency trains of stimuli, and a small but significant decrease in the amplitude of the second EJP in paired-pulse nerve stimulations, despite of insignificant changes in the amplitude of single EJPs, as compared to controls; there was also a moderate lengthening of the decay of both mEJPs and EJPs. These neuromuscular junctions do not show major morphological defects compared to controls (including the number of type Ib and type Is boutons and the area of the muscle surface), except that a minority of individuals present one or two Ib satellite boutons, which are composed of several smaller boutons budding from a single larger central bouton.

More than 65% of Dscam1^+t73.3 flies (containing 3 copies of Dscam1) have axonal targeting errors, and 30% have multiple errors in their arbors. They also show a significant increase in the number of ectopic branches in their pSc axonal arbors.

Following stimulation of the posterior scutellar bristles, Dscam1^+t73.3 flies (containing 3 copies of Dscam1) show a significantly reduced cleaning response compared to controls.