Again, it's not a single gene alone that determines sex. Changing any single gene can give interesting results if that gene is important to development of something. But the effects of genes are more subtle than you're giving them credit for.
Sex is not a switch between Male and Female. There isn't a magic gene that turns on the switch between the two.
Children are basically androgenous. Aside from genitalial differences, they're just about identical. When puberty hits, it's the hormones that really cause the differences between the sexes.
So if you want a 'magic bullet' that seperates the sexes, it's got to be estrogen (and the related hormones) and testosterone (and the realted hormones). But those come from the genitals, so they are only indirectly effected by the genes.
Again, the sexes are more subtle than you give them credit for.