midterm 2 W'10 KEY

midterm 2 W'10 KEY - KEY BICD100 Midterm 2 1 In a species...

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KEY 1 BICD100 Midterm 2 2/17/10 1. In a species of cats, eye color can be gray, blue, green or brown. Lines that are true-breeding for each eye color have been established. Results of crosses between individuals from these true-breeding lines are as follows: Cross # eye colors of true-breeding parents: F1 progeny eye colors: 1 green x gray all green 2 green x brown all green 3 green x blue all green 4 gray x brown all green a. Which of the following are demonstrated by the results shown in the table above? Circle all that apply (12 pts): >i. dominance ii. pleiotropy >iii. complementation iv. epistasis v. variable expressivity vi. incomplete penetrance b. Matings between male and female F 1 progeny of cross 4 produced 100 F 2 cats as follows: 59 had green eyes, 16 had gray eyes, 20 had brown eyes, and 5 had blue eyes. When blue-eyed cats from this F 2 population were crossed with cats from the true-breeding blue-eyed line, all the progeny had blue eyes. Based on these results, if male and female F 1 progeny of cross #3 are mated with each other, what eye color phenotypes do you expect to find among the F 2 progeny (8 pts)? The information provided tells you that gray and brown are both recessive to green, and that individuals homozygous for both the gray and brown eye mutations have blue eyes. You can infer this because you see blue eyed cats at approximately the frequency expected for double homozygous recessives in the F2 population derived from cross #4. Since the blue-eyed F2 cats x true-breeding blue eyed cats produce only blue-eyed progeny (lack of complementation), true-breeding blue eyed cats are also double homozygous recessive for brown and gray eye color alleles. So the green-eyed F1 progeny of cross #3 are heterozygous for both gray and brown eye color alleles, and when they are crossed together you will see green eyes (about 9/16), brown eyes (about 3/16), gray eyes (about 3/16) and blue eyes (about 1/16) in the F2 generation. c. Is an epistasis relationship indicated by the information provided in part b, above? If so, what is the relationship (which eye color is epistatic to which?) (6 pts) No. Double homozygous recessives have blue eyes (if there were epistasis, the double homozygous recessives would look like one or other of the single homozygous recessives). d. Are the genes determining gray and brown eye color more likely to function in the same biochemical pathway, or different pathways, and why (in one sentence) (6 pts)? Different pathways, since the double mutant phenotype produces a novel phenotype not seen in either single homozygous recessive.
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KEY 2 e. Using the data provided in part b, conduct a chi squared test to determine whether the gray and brown eye color genes are linked. Include in your answer your hypothesis, the value of chi squared, the associated p value (see table below), and your conclusion (linked or unlinked?). If the genes are linked, what genetic distance is indicated? (13 pts) Hypothesis: gray and brown eye color genes are unlinked (genes assort independently)
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This note was uploaded on 08/19/2010 for the course BICD bicd 100 taught by Professor Soowal during the Winter '08 term at UCSD.

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midterm 2 W'10 KEY - KEY BICD100 Midterm 2 1 In a species...

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