My sister dislikes chocolate icecream

[Imparcticle]

Consider this situation:
1.)I like chocolate icecream.
2.)My sister dislikes chocolate icecream, but prefers vanilla icecream.

I was wondering, why do people dislike or like something? Does one person get a stronger synaptic charge of seratonin (I hope that's the right neurotransmitter; if it isn't, I'm referring to one of or the one that deals with pleasure sensations. ) while the other person gets a lower charge? I am relating this to how addictions are contracted neurologically(such as those to drugs).

 

[fafalone]

While serotonin is related to overall mood regulation, acute pleasure is more related to dopamine receptors (and since you mention addictions, CNS mu/kappa opiate receptors) where the chemicals released are endorphins and enkephalins.

This seems to be more of a result of the pathway formed with the initial exposures to a substance. Consider studies where rats injected with a nauseating agent after eating an otherwise beneficial food will always avoid that food in the future, even after only one incident. While the regulation system is far more complex, it would seem to operate under the same principal.
As for predetermined likes and dislikes, the best cause is likely similar substances. When dealing with addictions, you'd be hard to pressed to find someone who doesn't derive pleasure from dopamine reuptake inhibitors and opiate agonists who doesn't also have a very bothersome negative physical reaction either every time or the first few times... these are a consequence of the mind liking something or not; but not a cause. Addiction therefore is not a consequence of this, but a desire to recreate the high levels of pleasure chemicals. Physical addiction only happens after psychological addiction, and the vast majority of substances (like ice cream) never progress to physical addiction.
So the cause of dislikes is largely psychological, relating to the experiences around the initial exposure and other indirect opinions of the mind evolving from early situations involving the substance.