Wincest is best Cest :3

Incest. I like it.

It wouldn't be your sister/brother/whatever if you were fucking your sister. Say you were a literal motherfucker however. If you were able to impregnate your mother with the same exact genes as your father gave to you, then that MIGHT technically be considered another blood sibling. If the genes aren't the same however, it would just be your child/half-sibling.

Mother + Father = Doughter and Son
Father + Dougter = Son (2)
Mother + Son = Dougter (2)
Son (2) + Doughter (2) = Im Out xD

This is a Story of TV in the past by RTL and Judgment... im Out by the first 5Min off Talkin btw 45min a episode and this going more crazy than I have described here.