A targeting vector was designed to insert a loxP site upstream of the coding sequence in exon 1, followed by an frt-flanked neomycin resistance (neo) cassette and a second loxP site upstream of exon 2 of the wntless homolog (Drosophila) (Wls) gene. Flp mediated recombination removed the neo cassette leaving the coding sequence of exon 1 floxed. (J:164701)