Based on the research, many scientists believe genetic predisposition along with a person's environment (including parental/social influences, available foods/nutrition) play an equal role in a human's development whether it be body fat, physical or mental prowess, athleticism, etc. In other words, no one is a prisoner of their genes. Just because you have genes related to becoming overweight or having the potential to becoming a elite endurance athlete, neither will happen unless you make it happen. In the former, you must eat poorly compared to movement and in the latter, you must be exposed to sports and then want to train to become an elite athlete. Below is a link to two articles regarding youth athletes, windows of growth and genetics:
Optimal Health for Maximum Growth in Young Athletes
http://www.dotfit.com/content-5386.html
Weight Gain & Athletic Performance
http://www.dotfit.com/content-5388.html