Boys who carry a particular variation of the gene Monoamine oxidase A (MAOA) often called as warrior gene are more likely to join gangs and be among their most violent members, according to a study from a Florida State University.
Monoamine oxidase A gene affects levels of neurotransmitters in the brain such as dopamine and serotonin that are related to mood and behaviour, and those variants that are related to violence are hereditary.
This effect of the gene applies only to males because of its location on the X-chromosome. Males, who have one each of X-chromosome and Y-chromosome, possess only one copy of this warrior gene, while females carry two having two X-chromosomes. Thus, if a male has an allele (variant) for the MAOA gene that is linked to violence, there isn’t another copy to counteract it. However, females have two copies, so even if they have one risk allele, they have another that could compensate for it. This is why the MAOA effect has only been detected in males.
Participants were drawn from the National Longitudinal Study of Adolescent Health of 1155 females and 1041 males, and the low MAOA activity alleles conferred an increased risk of joining a gang and using a weapon in a fight for males but not for females. Moreover, among male gang members, those who used weapons in a fight were more likely to have a low MAOA activity allele when compared with male gang members who do not use weapons in a fight.
http://www.comppsychjournal.com/article/S0010-440X%2809%2900049-2/abstract
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