Masha Gessen discovered through genetic testing that she had the dreaded BRCA1 genetic mutation--the same mutation made famous recently by Angelina Jolie, which predisposes women to ovarian and breast cancer. As Gessen wrestled with a wrenching personal decision--what to do with such knowledge--she explored the landscape of a brave new world, speaking with others like her and with experts including medical researchers, historians, and religious thinkers.Blood Matters is a much-needed field guide to this unfamiliar and unsettling territory. It explores the way genetic information is shaping the decisions we make, not only about our physical and emotional health but about whom we marry, the children we bear, even the personality traits we long to have. And it helps us come to terms with the radical transformation that genetic information is engineering in our most basic sense of who we are and what we might become.