Enhancer trap expression is observed in a 6 developing muscles in A1-A7 in the embryo. It is also observed in four pairs of cells associated with a subset of PNS neurons in each abdominal hemisegment. Two are associated with the dendrites of two es neurons of the dorsal cluster and two with the dendrites of two es neurons of the lateral cluster. These cells may be tormogen and trichogen accessory cells.
This chromosome carries an insertion approximately 4.5kb downstream of the ap transcription unit, unrelated to the ap phenotype: 80 independant excision derivatives (60% of which were homozygous viable and 40% of which were recessive lethal) retained the ap41F phenotype.