A human FGFR3 cDNA (NM_000142) with a glycine to arginine substitution at amino acid 380 (G380R), a FRT-flanked neomycin selection cassette, and a loxP site replaced a part of exon 2 to exon 17 of the mouse gene. Flp-mediated recombination removed the neomycin selection cassette. (J:287271)