I have found out that the children inherit the parent's artificial changes that aren't part of their genes.  Such as using a mirror to change their hair color.
I had a girl in her teens turn her natural hair color which was brown hair to black hair with some pink highlights by just using the mirror.  Then when she had a child of her own, a daughter.  The daughter ended up with black hair and pink highlights.

Genetics in sims 3 are no longer just from mom and dad, but also grandparents and anyone else in the family.