Scientists find predisposition for skinny jeans is in the genes. Your friend can eat whatever she wants and still fit into her prom dress, but you gain five pounds if you just look at that chocolate cake. Before you sign up for Weight Watchers and that gym membership, though, you may want to look at some recent research and save yourself a few hundred dollars. A woman’s waistline may have less to do with rigorous exercise and abstaining from sweets than it does with the genes of her parents.