The Slp gene is normally expressed in male mice, but it is expressed in females in the strains FM, LG, NZB, and PL due to a mutation in the rsl gene(s). The rsl (regulator of sex limited protein-Slp) phenotype is attributable to mutations in both the Rsl1 and Rsl2 genes. Both a small deletion of Rsl2 and a G-to-T transversion mutation that affects transcript splicing of Rsl1 appear to affect sexually dimorphic expression of male-specific genes, although only the mutation in Rsl1 appears to cause the loss of sex-limited expression of Slp.