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The Genetics Revolution PROBLEMS In each chapter, a set of problems tests the reader’s comprehension of the concepts in the chapter and their relation to concepts in previous chapters. Each problem set begins with some problems based on the figures in the chapter, which embody important concepts. These are followed by problems of a more general nature. WORKING WITH THE FIGURES 1. If the white-flowered parental variety in Figure 1-3 were crossed to the first-generation hybrid plant in that figure, what types of progeny would you expect to see and in what proportions? Answer: You would get a 1:1 ratio of purple to white. This is because the first-generation hybrid plant has one copy of the purple allele and one copy of the white allele, and as a result, 50 percent of the gametes would carry the purple allele and 50 percent of the gametes would carry the white allele. The white-flowered parental variety has two copies of the white allele, and all the gametes produced from the white plant will carry the white allele. Hence, a cross between the two would produce a 1:1 ratio of purple to white. Hybrid plant P/p ¥ white plant p/p Gametes 50% P 50% p ¥ 100% p 50% P/p : 50% p/p Purple : white 2. In Mendel’s 1866 publication as shown in Figure 1-4, he reports 705 purple (violet) flowered offspring and 224 white-flowered offspring. The ratio he obtained is 3.15:1 for purple:white. How do you think he explained the fact that the ratio is not exactly 3:1? Answer: This depends on the sample size. When the sample size was large, the proportions were close to 3:1 (e.g., for round and wrinkled seeds the ratio was 2.95:1 and the total population size
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