Fig. 4. The ref-2(mu218) mutation prevents LIN-39 and MAB-5 from canceling each other’s activities in males. The indicated mutants were stained with MH27 in early L2 to score Pn.p cell fusion in males. White circles indicate unfused Pn.p cells, short horizontal lines indicate Pn.p cells that have fused with hyp7. Hox gene expression patterns in each set of Hox mutant strains are indicated above each set of genotypes. Alleles used: lin-39(n1760) and mab-5(e2088), both null mutations, and mab-5(e1751), in which wild-type mab-5 is misexpressed in all Pn.p cells. All strains also harbored the him-5(e1490) mutation to generate males. At least 50 worms of each genotype were scored. All phenotypes listed are 100% penetrant except for: in mab-5(e1751); him-5(e1490) worms, P1.p fused with hyp7 in 1/52 worms and P3.p remained unfused in 1/52 worms, and in mab-5(e1751); him-5(e1490); ref-2(mu218) worms, P6.p fused with hyp7 in 1/51 worms.