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.