If type were purely genetic, we would have evidence of this. From all appearances, this is not the case.
Well, there HAS to be a correlation between your parent's type and yours - after all, it's genes we're talking about. And while it strongly depends on how they raise you, at least S/N must be passed on. I grew up with both my parents having full time jobs - my father sailed the seas and was gone for like 5-6 months, while my mother worked in our ministry of education. Being an only child (though somewhere at the age of 12 I found out I have a much older brother from my father's previous marriage) and not going out much, combined with my natural impressionable mind, I grew up to be a strong introvert, and while I thought I was intuitive, it's now clear to me I'm much more sensory-oriented. I was also very judging, because I got noone around most of the time to perceive things from. I had plenty of encyclopedias around, read most of them and thus get in love with facts and develop my Thinking side, and since I was mostly alone my Feeling side did not develop well. Through my teenage years I was naturally rebelling and now I'm guessing I made way for my tertiary and inferior functions to shine, thus falling in an INFP/INFJ/INTJ states. Then I fell in love and started a 7-year-old relationship which turned my world around, going through ultimate bliss and living hell, it stressed me out and almost made me go insane. It's over for more than 2 years now, I've already finished my degrees and I'm working for almost 2 years now. Things are finally coming to a sensible state and I see myself as a very ISTJ person.
From what I received as answers from my parents, they both score ISTJ on tests, but while my father is very ISTJ, I start to think my mother is not really one. She is definately Sensing and Judging, but she fluctuates from extrovert to introvert and thinking to feeling states. I have no clue how they managed to sustain their relationship, but I guess the Si bonds them well. And that should the major function I've inherited from them.
So from my point of view if you're primarily raised by your biological mom and she has high Si, chances are you'll have high Si too.
As this site is lacking an editing ability, I can't edit my former statements.My Mother is ESFJ
My father is INTJ .... I'm much more like my father is most areas.