A gene trap vector, pGT01xf, containing the beta-geo reporter gene (beta-galactosidase and neomycin resistance fusion gene) was inserted into intron 1 of the Ash1l gene. Immunohistochemical analysis of uterus tissue from 3 and 4 week old homozygous females and epididymis from homozygous males also shows diminished Ash1l protein. (J:222720)