They can always develop differently, due to interactions.
Also; you don't have to follow the alignment chart exclusively. It's a guideline, and there will always be people that argue as to which comic char is what align, or which movie char is which align, etc.
Mainly think how your char reacts to laws, and then ethics/morals. Those are the axes. (Axis'?) And you don't have to be extreme in them, either. Not everyone follows /every single law/, and not everyone will always do an evil deed.
The most difficult part about morals, is even a man labeled as evil, could be doing something that is good in his view. So this one is mostly your perceptions of things; though I suppose when one asks for alignment, they ask for what others would see you as. It's.... complicated.