I really apologise for slow updates at the moment. A-levels are approaching and I always seem tired. Anyway, on with the chapter.
Another common background story is that a family member is a scientist. As in, mad scientist kind of scientist. Honestly, I think this is just overused rather than applies to a Mary-Sue. It only becomes Mary-Sue when they are the victim of an experiment.
There is a saviour to this though. If you want to write this background, to make the effected character less Mary-Sue, try making the experiment go wrong, have the experiment physically or mentally damage them, or simply have them hate everything about it. Just a suggestion.
I felt that it was too overused and that's why I really had the pop in a chapter here.