Three genes whose mutations lead to altered behavioral phenotypes are $**$MAOA$**,**$SLC$6$A$4**,$ and $**$BNST$3**.$

$1.**$MAOA $($Monoamine Oxidase A$)**$: This gene encodes an enzyme responsible for breaking down neurotransmitters like serotonin, norepinephrine, and dopamine. Mutations in the MAOA gene can lead to increased levels of these neurotransmitters, which have been associated with aggressive and impulsive behaviors. Individuals with certain MAOA mutations may exhibit heightened aggression or antisocial behavior.

$2.**$SLC$6$A$4($Serotonin Transporter Gene$)**$: This gene encodes a protein that regulates serotonin levels in the brain by facilitating its reuptake. Variants in this gene, particularly the serotonin transporter polymorphism $(5-$HTTLPR$),$ have been linked to altered stress response and mood disorders. Individuals with certain SLC$6$A$4$ genotypes may experience increased anxiety, depression, or mood fluctuations.

$3.**$BNST$3($Bradford Negative Sex Behavior$)**$: This gene is involved in the sexual differentiation of brain structures. Mutations have been associated with altered sexual preferences and behaviors. In animal models, changes in BNST$3$ expression can result in variations in mating behaviors or sexual orientation.

These genes underscore the interplay between genetics and behavior, highlighting how specific mutations can influence psychological and social outcomes.