Beginning Friday, shoppers at more than 6,000 drugstores will be able to pick up a test to scan their genes for a propensity for Alzheimer’s disease, breast cancer, diabetes and other ailments. The test also claims that it can give a sense of whether the user has a propensity for obesity or psoriasis, or may be at risk of going blind. The over-the-counter test marks the first foray of personalized genomic medicine into the corner drugstore.