The addition of communspecified to robounspecified embryos does not affect the number of commissure crossing the midline. The addition of communspecified to sliunspecified mutants has no effect on the sliunspecified phenotype.
Some axons can cross the midline in communspecified kusunspecified double mutant embryos, but in most neuromeres the comm mutant phenotype is epistatic to the kus mutant phenotype. However, if commissural axons have crossed the midline, then this neuromere shows a kus mutant phenotype. Commissures are formed in communspecified sliunspecified double mutant embryos but in an irregular pattern.