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Look at it this way: if we didn't have a genetic code we wouldn't exist. If there wasn't an environment we wouldn't have anywhere to exist. Your genetics and environment interact, therefore, to produce you.

Two important terms to remember are Genotype and Phenotype. Your genotype is your actual genetic code and your phenotype is the manifestation of your genetic code. Huh? Consider this example: A thousand years ago people were, on average, a lot shorter. If you go to any of the ancient buildings in Europe, for example, you will notice that the doors are much shorter than they are today. What can we conclude from this? Perhaps humans have evolved over the last thousand years to be taller. That is, the human genotype has changed over time, allowing us to play basketball more effectively. Or maybe there is another reason. Perhaps the people of a thousand years ago had the genes to be as tall as people today, but there was something about the environment that prevented them from reaching their genetic potential. That is, the people of a thousand years ago may have had the genotype to be tall, but their phenotype was short. Allow me to offer the standard suggestion for why this is the correct explanation. Medical science has shown that poor nutrition during childhood will stunt a person's growth. The diet of people living in, say, Europe one thousand years ago wasn't all that great. Unless you were part of the social elite you probably had barely enough food to survive on and the food you did have wasn't going to be particularly rich on the proteins and vitamins needed for skeletal and muscular development and growth. As dietary nutrition has improved in Western countries over the last couple of centuries we have seen a corresponding increase in the height of the people living in these areas. Hence, a person's diet (i.e., the environment) can affect how their genetic code is manifest (i.e., how tall they get).