A lox71 site was inserted upstream of exon 2 and an FRT flanked neo cassette, 2A-tdTomato gene and lox66 site in inverse orientation were inserted downstream of exon 2. Flp mediated recombination removed the neo cassette. In the absence of cre-mediated recombination the tdTomato reporter is not expressed. Following cre-mediated the tdTomato reporter is expressed and exon 2 is placed in inverse orientation. The cre-mediated inversion is irreversible. (J:229605)