Imprecise excision of the P{EP} element, resulting in a 3428bp deletion that removes the entire Amph first exon (deletion extends from -1925 to +1502, coordinates relative to the first nucleotide (+1) of the first methionine of the Amph cDNA). Imprecise excision of the P{EP} removes 1113 nucleotides downstream from the initiating ATG completely removing the first exon of Amph.