If a black dog and a white dog have puppies, what color will the puppies be? Genetic scientists have been trying to answer this question for hundreds of years. Genetics is the science of heredity—how traits are passed from parents to offspring. One of the first breakthroughs came from Gregor Mendel, a nineteenth-century monk who spent eight years breeding thousands of pea plants. Pea plants might seem pretty different from dogs, but on a microscopic level, they have a surprising amount in common. Genetic pioneers of the twentieth century unlocked the secrets of DNA, the molecule that holds heredity information for all life-forms. Thjis book tells the story of how scientists cracked the code of life and revolutionized molecular biology.