LoxP sites have been inserted into introns 1 and 3. A single FRT site in the 3' untranslated region (UTR), just 5' of the Pgk-neo cassette, marks the former site of a neomycin selection cassette that has been deleted by flp recombinase. Crossing mice bearing this allele with Cre recombinase-expressing mice will delete exons 2 and 3, which contain the entire homeodomain. (J:94077, J:260050)