P{RS5} insertion in the first intron of Su(var)2-1; this results in aberrant splicing - the Su(var)2-1 5'UTR is spliced to the 3' splice acceptor site of the second exon of the w gene in the P{RS5} element, resulting in a chimeric transcript consisting of the Su(var)2-1 5'UTR and the second exon of the w gene.