ch23 - Chapter 23 23.1 If heart disease is considered to be...

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Chapter 23 23.1 If heart disease is considered to be a threshold trait, what genetic and environmental factors might contribute to the underlying liability for a person to develop this disease? ANS: Some of the genes implicated in heart disease are listed in Table 23.2. Environmental factors might include diet, amount of exercise, and whether or not the person smokes. FEEDBACK: 23.1 DIFFICULTY: easy 23.2. A wheat variety with red kernels (genotype A A B B ) was crossed with a variety with white kernels (genotype AA BB ). The F 1 were intercrossed to produce an F 2 . If each primed allele increases the amount of pigment in the kernel by an equal amount, what phenotypes will be expected in the F 2 ? Assuming that the A and B loci assort independently, what will the phenotypic frequencies be? ANS: 1/16 red; 4/16=1/4 dark pink; 6/16 pink; 4/16=1/4 light pink; 1/16 white FEEDBACK: 23.1 DIFFICULTY: medium 23.3 For alcoholism, the concordance rate for monozygotic twins is 55 percent, whereas for dizygotic twins, it is 28 percent. Do these data suggest that alcoholism has a genetic basis? ANS: The concordance for monozygotic twins is almost twice as great as that for dizygotic twins. Monozygotic twins share twice as many genes as dizygotic twins. The data strongly suggest that alcoholism has a genetic basis. FEEDBACK: 23.1 DIFFICULTY: easy 23.4. The height of the seed head in wheat at maturity is determined by several genes. In one variety, the head is just 9 inches above the ground; in another, it is 33 inches above the ground. Plants from the 9-inch variety were crossed to plants from the 33-inch variety. Among the F 1 , the seed head was 21 inches above the ground. After self-
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fertilization, the F 1 plants produced an F 2 population in which 9-inch and 33-inch plants each appeared with a frequency of 1/256. (a) How many genes are involved in the determination of seed head height in these strains of wheat? (b) How much does each allele of these genes contribute to seed head height? (c) If a 21-inch F 1 plant were crossed to a 9-inch plant, how often would you expect 18-inch wheat to occur in the progeny? ANS: (a) 4; (b) 3 inches; (c) frequency of 1/4. FEEDBACK: 23.2
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This note was uploaded on 11/26/2011 for the course BIOLOGY 2c03 taught by Professor Dej during the Spring '11 term at McMaster University.

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ch23 - Chapter 23 23.1 If heart disease is considered to be...

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