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. (a) What are the genotypes of the woman, her father, and her mother?
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This note was uploaded on 01/26/2011 for the course BIOLOGY 4003 taught by Professor Matthews during the Spring '10 term at Minnesota.

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

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