An IRES-cre/ERT2 cassette followed by a Frt-flanked neo-selection cassette was inserted into exon 7 of the Car1 gene by homologous recombination in ES cells. Correctly targeted ES cell clones were injected into C57BL/6 blastocysts. Mice were crossed to Flp-expressing mice to delete the neo cassette. (J:238627)