(SPOILER FOR SEASON 5)

I was just watching S2e17 of PB and T-Bag just told Susan that he was not able to procreate, or have kids. I haven't seen all of season 5, but I know that Whip is T-Bag's son. Can someone explain how Whip is T-Bag's son if he can't have kids? Did they explain this in the show?