A loxP site was inserted upstream of exon 3 and a floxed pgk-hygromycin cassette was inserted downstream of exon 3 via homologous recombination. Quantitative PCR and immunoblot analysis indicate a decrease in mRNA and protein expression in the inner ear of homozygous mice. Expression of Gjb2 mRNA and protein are also reduced in the inner ear of homozygous mice. (J:193913)