I would say there's a genetic tie still, though. It doesn't mean no one in future generations can get them at all, of course. It does mean that there are similar skin types, pregnancy trends and tendencies, etc, that may be passed on....making it more or less likely to get them. In your case, sure the women on one side of the family may not have had them, but what about your dad's mom? Or was your body type and pregnancy similar to your mother's/sister's or did you grow faster/bigger/etc?I really would disagree about stretch marks being genetic.