The endogenous allele was disrupted by the insertion of a vector containing exons 9 through 13, selection genes, and a 300 bp gap in intron 11. Homologous recombination of the vector results in double stranded gap repair, producing an allele in which exon 13 is followed by the selection genes and duplicates of exons 9 through 13. Transcript was undetected in homozygous mutant mice by RT-PCR analysis of gonad and spleen tissue. Expression of Vrk2, the adjacent locus, was unaffected.