It could be as simple as antecedent recessive genetic traits. I've yet to see anything about the grandparents or any other extended family members regarding Zoe, but you see much of the extended family of the Adamas.
However it has already also occurred to me that she may be adopted, or that her father is not really who he appears to be. This could be because the father was sterile (she may have even been implanted into the mother), or because of an affair. (Then again the mother could have been infertile and it was a procedure which was later transferred to her womb.)
I'm also, as much as I hate to admit this, but given the nature of BG, and given the nature of how the father has been acting in background - pretty well convinced that the father knew far more about what Zoe was up to, her possible associates, and may have even known of her involvement with the STO than he has thus far let on.
I didn't get to see the Friday night episode, I watched Absolute Justice with the wife and kids. But I'll try and catch it in reruns.
But the relationship between the father and daughter seems suspect to me in more than one way. (I'm not saying Graystone didn't love her, I'm saying it is a far more subversive relationship I suspect that immediately meets the eye. Just a detective's intuition. If I were investigating the case I'd start there, not with the mother.)
I also wouldn't be surprised if she were someone else's genetic daughter.
But in any case I instinctively feel there is much left unexposed at this point regarding that family and their relations with one another. Too much is fuzzy and out of place.