The targeting vector is designed with (from 5' to 3') a CMV-IE enhancer/chicken beta-actin/rabbit beta-globin hybrid promoter (CAG), a loxP-flanked STOP cassette, an FRT-flanked dTomato (dimer Tomato) sequence (dTomato is a DsRed variant that is reported to be a somewhat slow-maturing dimer with low acid sensitivity)), an EGFP, and a Neo-polyA cassette. (J:101977)