Will your son join a gang?

The answer may well be in his genes.

A new study conducted by researchers at Florida State University found young men who carry a particular variation of the gene Monoamine oxidase A, or MAOA, are almost twice as likely to join gangs and use a weapon in a fight.

It also found gang members with the genetic variant, sometimes called the "warrior gene," were more than four times as likely to use a weapon in a fight, compared to gang members without that particular variant.

This is the first time a direct connection has been made between the MAOA gene and the selection of a violent lifestyle, said the study's lead author, Kevin Beaver, a biosocial criminologist at the university's college of criminology and criminal justice.

"The genetic variant was distinguishing the most violent gang members from the least violent gang members," he said.

"We were surprised and shocked about how strong the effect was."

Experts say the study, the latest in a burgeoning field that looks for links between genetic makeup and behaviour, will help researchers better understand why some people are drawn to a criminal lifestyle.

That, in turn, will result in more effective crime prevention and rehabilitation programs targeted to individuals and their particular risk factors.

Gail Anderson, a criminology professor at Simon Fraser University, said knowing the biological basis of behaviour is key to solving why some people turn to crime.

"It doesn't mean that biology acts on its own," she said, "but it means that it is one small part of the puzzle. And if you are ignoring one small part of the puzzle, you are never going to finish the puzzle."

One of the jobs of MAOA in the body is to break down neurotransmitters, including dopamine and serotonin, which are important for regulating mood.

The variant of the MAOA gene associated with violent behaviour is found on the X-chromosome and is less effective at breaking down neurotransmitters.

Males, who have one X-chromosome and one Y-chromosome, have only one copy of the MAOA gene, which means a male is stuck with a low-functioning variant.

Females, who have two X-chromosomes, have two copies of the gene, one of which could compensate for a low-functioning variant.

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Beaver said this gender difference is one of the reasons his team did not find a link between the low-functioning MAOA variant and gang membership in females.

The study, published in the July issue of the journal Comprehensive Psychology, examined genetic and lifestyle data from more than 2,500 respondents to the (U.S.) National Longitudinal Study of Adolescent Health.