Regarding genetics vs. environment...
I have two adopted children (not biologically related). My oldest child, a daughter, came from a biological sib group of four. Their parents were so violently abusive to the children that each child (except for the oldest girl) were taken out of the home, shortly after birth; they never lived together as a family sib group. We adopted my daughter when she was three years old. She is now fifteen.
In the years that followed my daughters adoption, we kept in close contact with her siblings, and the families that had adopted them. It was COMPLETELY APPARENT to all of us, that ALL of the children had the same mannerisms, speech patterns, idiosyncrasies. The sib group is both male and female.
I have absolutely NO DOUBT that genetics is primary in our behavior. It wasn't until several years after my daughter came to live with us that I first noticed some new "Patterns" of behavior and mannerisms that she was picking up from me. However, the old mannerisms, etc. still prevail, in her personality.
Whenever my daughter and her older sister are together, I marvel, at the similarities between them. These go far beyond physical attributes.