The targeting vector from Fgfr2tm3.1Sor containing the L443A and R445A substitutions in exon 10 and a FRT-flanked neomycin-resistance gene followed by a loxP site located upstream of exon 10 is used to retarget ES cells derived from Fgfr2tm7.1Sor carrying the Y485F, Y788F and Y798F mutations. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:303230)