The targeting vector from Fgfr2tm5.1Sor containing the Y788F and Y798F substitutions in exon 19 and a FRT-flanked neomycin-resistance gene followed by a loxP site is located upstream of exon 19 is used to retarget ES cells derived from Fgfr2tm4.1Sor carrying the Y485F and L468L mutations. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:303230)