We're still just beginning to understand why some people become dependent on marijuana but others don't. Your genes could have a lot to do with it, a new study suggests.For the first part of the study , published online today in the Journal of Abnormal Psychology, researchers looked at genetic data from 1,558 Australians who reported both marijuana use and childhood sexual abuse.From that data, the researchers found an association between certain variations in participants' DNA and the likelihood that those participants would become dependent on marijuana: Cannabis dependence and childhood trauma were linked only for those participants who had this specific variation, even though everyone in the study used cannabis to some degree.We already know that childhood trauma — like sexual assault — is associated with a much higher risk of becoming dependent on a variety of substances, including alcohol and marijuana. But many people who have traumatic backgrounds are able to use those drugs without developing a dependence. These results suggest your genes may be the real catalyst in turning trauma plus marijuana use into actual dependence.In particular, the results suggest that having one specific variation (in a gene that codes for proteins involved in your body's endocannabinoid system ) may protect you from developing dependence, while having another variation may make you especially vulnerable. So, in the final phase of the experiment, the researchers wanted to know how that variation might affect your ability to deal with other stressful life situations.To determine this, they looked at the genetic and brain-imaging data of 312 undergrads. Here, participants had to do tasks that were designed to increase the activity in their amygdala, a brain area traditionally associated with our ability to process fear and anxiety.However, participants didn't show as much of an increase of activity in their amygdala if they had the protective genetic variation. This lower response suggests these participants had become habituated to the stress, the researchers concluded.But the study's authors emphasize that we're not at the point where we can "diagnose" whether or not someone will become dependent on pot just based on his or her genetics. There are still plenty of other factors at work here, and the very idea of marijuana dependence is still a controversial issue itself. But other recent research suggests that, as the use of both medical and recreational weed has increased, so has the prevalence of marijuana-use disorders. So now is the time to get the good stuff (data).