An IRES-cre was inserted into the 3' region of the Cgamma1 locus between the last membrane-coding exon and its polyadenylation sites. This targeting design allows for the expression from the locus of a bicistronic mRNA consisting of the Cgamma1 and Cre transcript. An FRT site flanked neomycin resistance gene cassette was removed via Flp recombinase expression. (J:109583)