It's more like DNA codes for potentialities (when it's not coding simple morphology, that is), while environment either encourages or inhibits that potential.

Let's say the DNA of a creature codes for it to be no taller than 6 feet, but no less than 5 feet. If it gets a decent diet and isn't exposed to nasty chemicals (alcohol or anything else), it's likely to hit its potential .. but if it doesn't, it might be stunted and only be five feet tall. The same goes for intelligence and other "soft" coded elements of a living thing.

Think on this: A sufficiently advanced and truly sentient/sapient robot would never refer to its programming limiting it from doing this, or forcing it to do things. It would say it "feels" right or wrong, and would probably deny its programming had anything to do with its decision-making ... in the same way humans don't think they have natural predilictions for or against things that influence their OWN behaviour sets ...