Imprecise excision of the P{XP} element that results in a 77bp insertion at the P{XP} site.
abnormal neurophysiology
Electroretinograms from t42A flies show a reduction in "on" lamina transients (5.6% vs 23.3% in wild type) and a reduction in "off" transients (3.9% vs 63.3% in wild type).