A loxP site was inserted upstream of exon 2. An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted downstream of exon 8. Cre-mediated recombination removed exons 2 through 8 and left the FRT-flanked neomycin resistance cassette intact. Fatty acid elongation activity towards C22-CoA is greatly reduced in the skin, brain and liver.