system
Given the following post, respond as if you're commenting on Reddit:
human
[GOT/ASOIAF] How does genetics work in this world? The Targaryen's don't have any phsyical ailments, the Lannister kids are 2/3 okay in terms of attitude and Gilly and Little Sam seem to be fine? Is it different in the books compared to the show?
gpt
A few things. 

It's not like incest automatically creates a toxic avenger. It only increases the chance of severe problems. And mostly if it builds up over generations. 

We don't know detailed medical profiles of the characters, they could have hidden problems that we don't see on the show or would only become
revealed in their older years. Assuming the characters make it to their older years. Most don't. 

Targaryens are known for having a 50/50 chance of kind of normal/batshit crazy. So there's that.