I'm not sure how much genetics enter into the equation... except that there is a 1:4 chance... mothers dominant, mothers recessive, fathers dominant, fathers recessive gene pool to draw upon. And with each generation, those odds get higher (or is it lower?).. for example, in my direct ancestry, theres a distant great, great (however many it was) uncle who grew to be 7' 10"..
He didn't have any children (and if you were a woman during his time, do you think you'd want to take the chance of bearing his children w/o the aid of any modern medical science? I think not).. Anyway, apparently the only iota of his genes we inherited was shoe size.. I'm a 14, my oldest son is now there and still growing... yet my youngest, who appears to be a carbon copy of me in all other aspects, has neither my height or my shoe size at age 19...
Why? I dunno... The whole nature Vs nuture debate comes into play. He was not exposed to the hard physical life I was during his formative years, and his diet and mine were/are vastly different. So, it just doesn't come down to one's ancestry/family genes. Which augments the theory that ones health HAS more than a passing influence on ones physical development...