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Chapter Education of a Scientist 1 There is a 5,000-year-old Persian seal inscribed with horses’ heads that shows a record of inheritance of mane and head shape through several generations. In England, Robert Bakewell (1725–95) founded a famous herd of longhorn cattle by inbreeding: mating animals that were similar in order to emphasize certain characteristics, such as size and color. In North America, Native Americans improved their maize crop by outbreeding—crossing two unlike varieties of corn to get a variety with the qualities of both. Sometimes these methods of selective breeding for inherited characteristics were successful. But sometimes the offspring would be more like one parent than the other, sometimes the offspring would be a mixture, and, sometimes, the offspring would be a “throwback” to a grandparent. Thus, selective breeding worked in practice, but the reasons for its success or failure were not understood. In 1865, a friar named Gregor Mendel explained in his writings how characteristics (in his writings, he called them “characters”) were inherited, how heredity depended on sexual reproduction, and how the inheritance of likenesses followed simple mathematical rules. This is the basis of the modern science of genetics . By following Mendel’s rules, it is possible to understand how the size of corncobs, the quality of a horse’s mane, or the color patterns of a cow’s coat are inherited. The rules of genetics that Mendel pioneered have been found to apply to all plants and all animals. But inheritance in humans is not as easy to study as it is

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