Actress Angelina Jolie has today written an op-ed in the New York Times explaining that she has opted to have a double mastectomy because she carries the hereditary BRCA1 gene, which she says increases her risk of breast cancer by 87%. Her mother died from breast cancer after a ten-year struggle at the age of 56. We asked an expert in breast cancer and genetics to explain more about the breast cancer genetic mutation and what it means for women.