Is every decision we make already "pre-programmed" because of DNA?
&quot;Do we have free will?&quot; It's a big question.
DNA (among other epigenetic factors) code for proteins, so ultimately it determine our cells, which in turn are responsible for our neurology, although how this translates to behavior is variable depending on factors beyond DNA@Remi.b's answer. De facto you're asking about the extent that our brain structure and neural activity determines our conscious stream. This boils down to &quot;Do we have free will?&quot;. That question historically was only accessible to philosophers. It is now accessible (but not completely answerable) to biologists, more specifically neuroscientists. It's a great question, but is still open to a lot of subjectivity.
An evolutionary explanation.
Anil Seth, professor of cognitive and computational neuroscience at the Sackler Centre at the University of Sussex, gives a very good answer to the question at 25:44 in this BBC Life Scientific interview.

We are determined to have it in both senses of the word...
Yes, we do have free will because we can behave the way we wish to behave. We cannot decide what to will.

Paraphrasing the guts of the answer: it's very important for the brain to differentiate between internalized experience, and reflex.
Reflex, such as placing your hand on a hot stove, never reach the &quot;conscious stream&quot;. These have an obvious correct choice; in this case, removing the hand from a hot stove is clearly the right choice, every time.
Then there is internalized experience. Complex problems have many potential losses and gains. To cope with this, the brain needs to internalize, reflect, and is taking note and making a plan; the sensation of free will. By taking note of that situation within it's context and the plan, we can perhaps change our actions the next time we encounter a similar event so that we can optimize our choices to attempt to cause the least damage to ourselves and/or maximize the benefit.
How is learning achieved.
We have established that there is a need for new memories to form in order to solve complex problems. Long term memories are the result of new physical synaptic connections in the brain. This connection endures whether it’s being used or not.
Psychologists put these into two broad types are two kinds, implicit (akin to reflex; how to read, how to play your favorite song on an instrument etc.) and explicit (the things we are consciously aware of). Explicit memory comes in two forms: episodic and semantic (Tulving, 1972). (i) Episodic memory includes experience. For example, that time you planted some seeds and a potato grew. (ii) Semantic memory is abstract to your own experience. Something more like &quot;Primordial potatoes originated in southern Peru&quot;.

To bring this back to the original question &quot;Is every decision we make already pre-programmed because of DNA?&quot; It's long winded. Our choices are built upon the results of our past choices in a given environment. We are able to make these choices, to an extent depending also on other variables, because of the products and machinery encoded in our DNA.
The philosophers answer
If this answer is a bit scary or makes your choices seem futile, you can simply sit around and do nothing instead of doing whatever you normally would do; it's your choice.
See a similar question answered from a different perspective over at Philosophy.SE.