The 20,000 or so genes in the human genome encode a great diversity of proteins, which carry out many activities. Blood clotting, muscle contraction, digestion of food and absorption of its nutrients, and cellto-cell communication are a few of the vital functions of proteins in a human body. Yet, a single pattern of information flow underlies the making of proteins from genetic instructions. Understanding what a gene does when it is working, and what happens when it is not, can suggest ways to treat genetic and other types of diseases.