Since the mice used in our study were a cross between C57BL/6 (B6) mice and DBA/2 (D2) mice, and thus, these B6D2F1 mice are heterozygous for B6 and D2 alleles at all loci in their genome, we can eliminate infertility susceptibility of either the B6 or the D2 background as the cause for fertility defects in Ces5a and Spint4/5 mice. This evidence concerns the gene SPINT4 and Infertility.