The difference between one personality and another is not determined by genes alone. Love’s got something to do with it too.
— Read on discovermagazine.com/2010/jun/15-brain-switches-that-can-turn-mental-illness-on-off
Epigenetics, modifications of DNA, but not the sequence of DNA, can have huge effects in the organism.
You can possibly turn mental illness genes off with epigenetic changes! Exciting!