Test Bank for Chapter 5: Extensions and Modifications of Basic Principles Multiple Choice Questions 1. The R locus determines flower color in a new plant species. Plants that are genotype RR have red flowers, and plants that are rr have white flowers. However, Rr plants have pink flowers. What type of inheritance does this demonstrate for flower color in these plants? a. Complete dominance b. Incomplete dominance c. Codominance d. Complementation e. Lethal alleles Answer: b Section 5.1 Comprehension 2. Interactions among the human ABO blood group alleles involve _______ and ________. a. co-dominance; complete dominance b. codominance; incomplete dominance c. complete dominance; incomplete dominance d. epistasis; complementation e. continuous variation; environmental variation Answer: a Section 5.1 Comprehension 3. In the endangered African watchamakallit, the offspring of a true-breeding black parent and a true-breeding white parent are all gray. When the gray offspring are crossed among themselves, their offspring occur in a ratio of 1 black:2 gray:1 white. Upon close examination of the coats, each hair of a gray animal is gray. What is the mode of inheritance? a. One gene pair with black dominant to white b. One gene pair with codominance c. One gene pair with incomplete dominance d. Two gene pairs with recessive epistasis e. Two gene pairs with duplicate genes Answer: c Section 5.1 Comprehension 4. Suppose that extra fingers and toes are caused by a recessive trait, but it appears in only 60% of homozygous recessive individuals. Two heterozygotes conceive a child. What is the probability that this child will have extra fingers and toes? a. 0.05 b. 0.10 c. 0.15 d. 0.25 e. 0.33 Answer: c Section 5.1 Comprehension 5. Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of a. variable expressivity. b. complete dominance. c. independent assortment. d. complementation. e. cytoplasmic inheritance. Answer: a Section 5.1 Comprehension 6. Achondroplasia is a common cause of dwarfism in humans. All individuals with achondroplasia are thought to be heterozygous at the locus that controls this trait. When two individuals with achondroplasia mate, the offspring occur in a ratio of 2 achondroplasia:1 normal. What is the most likely explanation for these observations? a. Achondroplasia is incompletely dominant to the normal condition. b. Achondroplasia is codominant to the normal condition. c. The allele that causes achondroplasia is a dominant lethal allele. d. The allele that causes achondroplasia is a recessive lethal allele. e. The allele that causes achondroplasia is a late-onset lethal allele. Answer: d Section 5.1 Comprehension 7. Crossing two yellow mice results in 2/3 yellow offspring and 1/3 nonyellow offspring. What percentage of offspring would you expect to be nonyellow if you crossed two nonyellow mice? Application 39. In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Rose crossed with pea produces 20 walnut offspring. a. RR pp × rr PP b. Rr pp × rr Pp c. Rr pp × rr PP d. RR pp × rr Pp e. Rr pp × Rr Pp Answer: a Section 5.2 Application 40. In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Pea crossed with single produces 1 single offspring. a. rr PP × rr pp b. RR Pp × rr pp c. Rr PP × rr pp d. Rr Pp × rr pp e. rr Pp × rr pp Answer: e Section 5.2 Application 41. In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Rose crossed with pea produces 2 walnut, 1 single, and 1 pea offspring. a. RR pp × rr PP b. Rr pp × rr Pp c. Rr pp × rr PP d. RR pp × rr Pp e. Rr pp × Rr Pp Answer: b Section 5.2 Application 42. In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Rose crossed with single produces 31 rose offspring. a. RR PP × rr pp b. RR pp × rr pp c. Rr PP × rr pp d. Rr Pp × rr pp e. Rr pp × rr pp Answer: b Section 5.2 Application 43. In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. Give genotypes for comb shape of the parents in the following cross: Rose crossed with single produces 10 rose and 11 single offspring. each extreme line are (theoretically) homozygous and isogenic. Therefore, variances in tail length observed within each line cannot be the result of variable polygenic genotypes. Section 5.5 Application 83. You are studying a coat color gene (B, brown) in Mexican bats. You have isolated a recessive allele (b) that causes yellow coat color, but you suspect that the phenotype may be sensitive to environmental conditions. To test your hypothesis, you examine the segregation ratio of phenotypes in F1 progeny from a cross between two heterozygotes. You do this once at normal laboratory temperatures (28C) and once at temperatures closer to their native habitat (34C) and record the following data: Brown Yellow 28C 153 47 34C 170 30 a. What ratio do you expect in each experiment if temperature does not affect the phenotype? b. What test can you use to determine if the ratio you observed is significantly different from the expected ratio? c. Using that statistical test, is either observed ratio more different from the expected ratio than one would expect from chance alone? If so, suggest a biological explanation. Answer: a. This is a simple monohybrid cross with brown dominant to yellow, so expect 3 brown:1 yellow. b. The chi-square test. c. The chi-square test for the treatment at 34C yields a value of 2 = 10.67, indicating a significant difference from the expected ratio of 3:1.