gfAPΔ5 flies perform no differently to wild-type flies in terms of flight, olfactory behavior, and in visual tests (although there is a slight difference in phototaxis assays compared to wild-type flies). However, in contrast to wild-type flies, these flies fail to jump in response to a lights-off stimulus.
gfAPΔ5 flies have a defect in the jump circuit between the peripherally synapsing interneuron (PSI) branch of the giant fiber and the dorsal lateral muscle (DLM) motor neuron. This is demonstrated by intracellular recordings of DLMs following giant fiber stimulation; while the DLMs of wild-type flies can follow stimulation frequencies of up to 100 Hz, gfAPΔ5 flies show little response in the DLMs even at a stimulation frequency of 1 Hz. The defects are specific to the synapses between the PSI and DLM motor neurons as the tergotrochanteral muscles are able to follow the giant fiber stimulation at 100 Hz without any problem. This phenotype can also be seen in gfA1/gfAPΔ5 transheterozygotes.
The tergotrochanteral muscle of gfAPΔ5 flies responds to low-strength electrical stimulation, which activates the elements presynaptic to the giant fiber, which in turn activate the giant fiber, with the short-latency response seen in wild-type flies, but fails to show the long-latency response.
Based on the extent of the jump circuit defect in gfA flies, the following alleles can be ranked from strongest to weakest as follows: gfAPΔ5 = gfAPΔEY6 > gfAPΔ41 > gfAPΔ14G.