Shows weak enhancement of the extra sex combs phenotype of Pc4. Viable in transheterozygous combination with E(Pc)1. Position effect variegation (PEV) at the w locus caused by In(1)wm4 is unaffected by E(Pc)rv10. PEV at the B locus caused by Dp(1;Y)BSCV is slightly suppressed by E(Pc)rv10.