A cassette consisting of mouse exon 1, EGFP reporter sequence, loxP site, 2A self-cleaving peptide sequence, human DDX25 cDNA containing an arginine to histidine substitution at amino acid 242, SV40 sequence, loxP site, FRT-flanked PGK-neomycin selection cassette, and third loxP site replaced exons 1-5 of the gene. Flp-mediated recombination removed the neomycin cassette. The R242H variant is found in Japanese infertile men. (J:291302)