After genetic testing revealed a heightened risk for breast cancer, Angelina Jolie had a precautionary double mastectomy. Alastair Grant/AP hide caption

itoggle caption Alastair Grant/AP

Each strand of DNA is written in a simple language composed of four letters: A, T, C and G. Your code is unique and could be used to find you. iStockphoto.com hide caption

itoggle caption iStockphoto.com