Your dad's family heritage

"What is it, daddy?" you ask, feeling slightly nervous. If you still had your ring on, you'd probably transfer back to your old body and let Phoebe deal with this.
"In this family we have an important tradition. Jennifer dear, you can explain, as we agreed," your father says.
"O-okay... so it's quite simple, really. Your father's family is quite special. They have certain, um, attributes that have been carefully selected for generations. Maybe it'll be better if you show her, dear," your mother says.

Harvey nods and without any warning he unzips his pants and drops them. To your horror, you see his monstrous cock, still flaccid, for the second time that day. You avert your eyes, shocked that your parents are showing you this and yet frozen in confusion as your mother continues to talk.

"Your father's family are physically elite, including, as you can see, down there. Every tenth generation, they integrate a new family's genes into their own. I was selected by him at a young age because, as I'm sure you know, I come from a family of geniuses," your mother continues.
"You're so smart, my dear," your father grins, slapping her ass.
"Now, the secret to your father's family is all to do with a mutation they have. With most people, if they breed with their relatives, their weak traits are generally revealed. In your father's family, the opposite happens. Weak traits are suppressed and strong traits are strengthened. Which means..." your mother explains, looking at you.

You feel a panic rising in your chest. The implication was clear, and you can see dad's cock begin rise already.