Final answer:
Boys with a gene producing lower levels of MAO-A have reduced aggression.
Step-by-step explanation:
Research conducted with boys who have a gene that produces lower levels of MAO-A, which has been associated with aggression, has found that these boys have reduced aggression. The gene MAO-A plays a role in the breakdown of neurotransmitters, including serotonin, which is involved in regulating emotions. Lower levels of MAO-A can result in an accumulation of serotonin in the brain, which can lead to decreased aggression.