Beginning Friday, shoppers in search of toothpaste, deodorant and laxatives at more than 6,000 drugstores across the nation will be able to pick up something new: a test to scan their genes for a propensity for Alzheimer's disease, breast cancer, diabetes and other ailments. The test also claims to offer a window into the chances of becoming obese, developing psoriasis and going blind. For those thinking of starting a family, it could alert them to their risk of having a baby with cystic fibrosis, Tay-Sachs and other genetic disorders. The test also promises users insights into how caffeine, cholesterol-lowering drugs...