The triumphs of recent biology - understanding hereditary disease, the modern theory of evolution - are all thanks to the fruit fly, the guinea pig, the zebra fish and a handful of other organisms, which have helped us unravel one of life's greatest mysteries - inheritance.Jim Endersby traces his story from Darwin hand-pollinating passion flowers in his back garden in an effort to find out whether his decision to marry his cousin had harmed their children, to today's high-tech laboratories, full of shoals of shimmering zebra fish, whose bodies are transparent until they are mature, allowing scientists to watch every step as a single fertilised cell multiples to become millions of specialised cells that make up a new fish. Each story has - piece by piece - revealed how DNA determines the characteristics of the adult organism. Not every organism was as cooperative as the fruit fly or zebra fish, some provided scientists with misleading answers or encouraged them to ask the wrong questions.