Knock-in construct in which a portion of a cDNA corresponding to exons 5-19 followed by a polyadenylation signal was inserted into the endogenous locus. This allele expresses a wild-type cDNA used as a control for Fgfr3tm1Cxd. A loxP flanked neomycin cassette also inserted downstream of the inseted cDNA was removed via Cre mediated recombination in the final allele. (J:52438)