I'm not sure about the DNA thingy though, maybe it has, but I think it's probably on what they see on their parents that is pass from generations to generations, not DNA per se. If you see you parents at a young age, have gambling sessions in your house (this is prevalent is Asian Culture, playing mah-jong). Definitely you can inherited this as you grow old. So it is still the environment that is the influencing factor and I think majority of gamblers some kind of interaction or exposed to gambling when they are very young. But we have a choice, whether to fall victim or not.
Well, i have observed this from my neighborhood, that most of them have turned into gamblers. Maybe heredity still counts as whatever the tree, so is the fruit. But having an environment that is full of gamblers may also have a big effect on the young ones. It's like their young minds have been motivated that gambling can make them rich, or the reason that they don't struggles in life. However, when they grow old and mature, they will eventually discover the real effects of gambling, and its their choice whether to do the same or just get rid of gambling.