A loxP site was inserted upstream of exon 12. An FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downstream of exon 13. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exons 12 and 13. Western blot analysis confirmed the absence of protein expression in the testes. (J:207846)