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Chapter 3 Answers to Homework Problems (1)

Chapter 3 Answers to Homework Problems (1) - Chapter 3...

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Chapter 3 Answers to Homework Problems 1, 3, 4, 5, 7, 10, 12, 16, 17, 19, 22, 23, 24, 25, 29 1. Questions and Problems, 3-1 On the basis of Mendel’s observations, predict the results from the following crosses with peas: (a) a tall (dominant and homozygous) variety crossed with a dwarf variety; (b) the progeny of (a) self-fertilized; (c) the progeny from (a) crossed with the original tall parent; (d) the progeny of (a) crossed with the original dwarf parent. Ans: (a) All tall; (b) 3/4 tall, 1/4 dwarf; (c) all tall; (d) 1/2 tall, 1/2 dwarf. 3. Questions and Problems, 3-3 A geneticist crossed wild, gray-colored mice with white (albino) mice. All the progeny were gray. These progeny were intercrossed to produce an F 2 , which consisted of 198 gray and 72 white mice. Propose an hypothesis to explain these results, diagram the crosses, and compare the results with the predictions of the hypothesis. Ans: The data suggest that coat color is controlled by a single gene with two alleles, C (gray) and c (albino), and that C is dominant over c . On this hypothesis, the crosses are: gray ( CC ) × albino ( cc ) > F 1 gray ( Cc ); F 1 X F 1 > 3/4 gray (2 CC : 1 Cc ), 1/4 albino ( cc ). The expected results in the F 2 are 203 gray, 67 albino. To compare the observed and expected results, compute χ 2 with one degree of freedom: (198 203) 2 /203 + (67 … 72) 2 /72 = 0.470, which is not significant at the 5% level. Thus, the results are consistent with the hypothesis. Note: The publisher’s answer has a mistake in it. As there are 270 progeny, the expected numbers from a 3:1 ratio are 202.5 and 67.5. It is best not to round these. Then, χ 2 = (198-202.5) 2 /202.5 + (72-67.5) 2 /67.5 = 0.1 +0.3 = 0.4. The ultimate conclusion is the same. The results are consistent with the hypothesis. 4. Questions and Problems, 3-4 A woman has a rare abnormality of the eyelids called ptosis, which prevents her from opening her eyes completely. This condition is caused by a dominant allele, P. The woman’s father had ptosis, but her mother had normal eyelids. Her father’s mother had normal eyelids.
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