Exon 5 and associated intronic sequence is replaced with a loxP site, the corresponding wild-type human exon 5 and associated intronic sequence, Lox2372 site, inverted exon 5 with a nucleotide substitution that results in the amino acid substitution of histidine for arginine at position 206 (R206H), loxP site, a small insert derived from rabbit hemoglobin beta intron 2, lox2372 site and FRT-flanked neomycin resistance cassette. Flp-mediated recombination removed the selection cassette. The R206H point mutation mimics one identified in humans as causing Fibrodysplasia Ossificans Progressiva (FOP). Prior to cre-mediated half of its transcripts lacked exon 5 resulting in a hypomorphic allele.