The construct incorporates an FRT-lacZ-loxP followed by a neomycin resistance cassette, SV40 polyA, a second FRT site and a second loxP site in intron 3. A third loxP site is inserted downstream in intron 5 (position 78855613). Flp-mediated recombination removed the FRT-flanked lacZ and neo cassette leaving exon 4 floxed. (J:101977)