Sex-determining factor which regulates hermaphrodite development. Expressed from early larval stages through to adulthood. Temperature-sensitive phenotype in which XX animals are self-sterile, do not produce spermatocytes, but ovulate and produce progeny when mated with males; XO animals develop as males, but some switch to oogenesis in later life. Animals do not produce fog-3 proteins responsible for controlling germ cell fate. RNAi-mediated knock-down results in 95% female progeny.