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# final - EXAM A ANSWER KEY PART I PROBLEMS 1 You are...

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EXAM “A” ANSWER KEY PART I PROBLEMS 1) You are studying the population in Iceland for X-linked alleles, and sampling experiments indicate that about 6% of the men have red-green color blindness (caused by a recessive, X-linked allele c ). Assume that the population in Iceland mates randomly. a. What are the frequencies of the X-linked allele for men and for women? b. What percentage of women is expected to be color blind? c. What percentage of individuals in the population is expected to be normal carriers for the color-blind allele? d. After two generations, what percentage of men in the population is expected to be color blind? To have normal vision? a. Let p and q equal the frequencies of the dominant and recessive alleles, respectively. The frequency of the color-blind allele in males = q (hemizygous) = 0.06, or 6%; and the frequency of the color-blind allele in females = q 2 (homozygotes) + 2 pq (heterozygotes) = (0.06) 2 + 2(0.06)(1 – 0.06) = (0.0036) + 2(0.06)(0.94) = 0.116, or 11.6%. (4 pt) b. The expected frequency of color-blind females ( cc ) in the population = q 2 = (0.06) 2 = 0.0036, or 0.36% of the population. (3 pts.) c. The population is assumed to be in H-W equilibrium with q = 0.06 and p = 0.94; therefore, the frequency of heterozygote carriers = 2 pq = 2(0.94)(0.06) = 0.113, or 11.3%. Note that all of these carriers with normal vision are women as only women can be heterozygous for alleles found on the X chromosome. (4 pts.) d. For a population in Hardy-Weinberg equilibrium, the allele (gene) and genotypic (zygotic) frequencies will NOT change from generation to generation. Therefore, because the frequency of the recessive allele ( q ) = 0.06 (or 6%), the frequency of color-blind males (XY) in the population will be 6%. Similarly, after 2 (or 3, or 4, etc.) generations, (1 − 0.06) or 94% of the men in the population are expected to have normal vision. (4 pts.) 2) You discover a certain species of weed growing in soil contaminated with toxic PCBs, and later determine that the PCB resistance is due to a single dominant allele. a. If 45% of the seeds from a randomly mating population of resistant weeds will germinate in contaminated soil, what is the frequency of the PCBresistance allele? b. Among all the plants that germinate, what proportion will be heterozygous?

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