A w^+mW.hs marker has been inserted into the Prestin locus, flanked by small duplications of the 5' end of Prestin exon 3 and the 3' end of Prestin exon 2. Each duplicated Prestin segment contains two engineered stop codons. Several transcripts are produced by the mutated locus, none of which are wild type: either they are very short, or splicing past the w^+mW.hs insert causes a frameshift leading to tandem stop codons near the 3' end of exon 2.