A brilliant and emotionally resonant exploration of science and family history. A vibrant young Hispano woman, Shonnie Medina, inherits a breast-cancer mutation known as BRCA1.185delAG. It is a genetic variant characteristic of Jews. The Medinas knew they were descended from Native Americans and Spanish Catholics, but they did not know that they had Jewish ancestry as well. The mutation most likely sprang from Sephardic Jews hounded by the Spanish...