It's the nature vs nurture situation. While the genetics of a person does control the physical traits he/she may develop, the environment also has a major role to play here. For instance, the person may have the genes for developing a tall height. If, however, that person is not provided with the right kind of nutrition and the right time, it is very likely that he/she will not grow as tall as they had the potential for. Similar explanation for non-physical traits.
This is not an 'either/or' type of argument. Genetics and the environment have a collective impact in shaping the person into who they are and while the balance may shift to one side or the other in certain cases, it does not cancel out or negate the other's effect.
