Epigenetics is the changes in certain conditions, such as PKU, a rare genetic learning disorder, can be detected and if detected in a child, a strict diet can make it so that it isn't developed.
A candidate gene is a gene that is believed to be a particular characteristic, such as the MAOA warrior gene, which people may use as an excuse once done a crime, a theory known as labelling theory, which removes responsibility.
Neurotransmitters are chemical messengers, with examples including Serotonin, which affects mood, Dopamine, which affects reward, and Melatonin, which affects sleep.