In psychology there is always the debate of nature vs. nurture. Few legitimate psychologists today would believe that our biology or our upbringing completely controls our behaviors. In some instances certain behaviors lean towards one or the other, but overall I'd suppose it's about fifty fifty.
In my psychology class, I learned it's about 70-30 genetic based-environmental, with much of the environmental influence coming from our peers and almost zilch from our parents (minus, of course, the fact that they decide where we live, which affects what peers we are involved with 
).
Don't know where the 70-30 figure came from - I think I've heard that for certain traits (Type A personality IIRC) but not an overall estimate. Also, I haven't heard anything about almost zilch coming from parents. That might have just been your professors beliefs. The classes I took just said that opinions vary on the subject among academics.
I was more talking about personality (extroversion, openness to change, neuroticism, agreeableness, conscientiousness) than some cultural traits. That figure came from
my textbook, by the way
Nature vs. nurture is pretty much what defines the difference between a sociologist and psychologist now, by the way... I just haven't had a sociology class yet. So, though it is different across disciplines, psychology has been trending more and more "physiological" these days.
