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Evolutionary Genetics Midterm 2006 Name Student # Signature The Rules: P1: /15 P2: /22 P3: /16 P4: /25 P5: /22 TOT: /100 (1) Before you start, make sure you’ve got all five pages of the exam, and you’ve written your name legibly on each one. (2) Show your work on calculation questions. Feel free to use the back of the paper if required, but make sure to tell us when to look on the back. Calculations are required for full credit where asked. (3) If a calculation question requires you to start with the result from a previous calculation, and you were unable to answer the earlier question, you may make up a reasonable number to start with and still potentially get full credit on the second question. 1. (3 points) True or False: "Evolution requires that some types of individuals are more likely to survive." 2. (3 points) True or False: "Because mutation rates are very low, mutation contributes little to the process of evolution." 3. (3 points) True or False: "The main difference between Darwin’s and Wallace’s views of evolution was that Darwin considered biogeographical patterns to be important." 4. (6 points) Provide three reasons why the frequency of allele A might increase from one generation to the next within a haploid population. [Explain each answer in one sentence.] a) Reason:______________ Explanation: ______________________________________ ______________________________________________________________________ b) Reason:______________ Explanation: ______________________________________ ______________________________________________________________________ c) Reason:______________ Explanation: ______________________________________ ______________________________________________________________________ Page 1 of 5 Evolutionary Genetics Midterm 2006 5. Name (10 points) In the Cody and Overton (1996) study, the authors found that Vp/Va (= volume of the pappus to the volume of the achene shown at left) was greatest for newly colonized islands and decreased over time since colonization, as shown in the graph to the right (note that “mld” denotes the mainland population). For island populations of the same age since colonization: QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. a) How would you predict the trends in Vp/Va to differ on bigger islands versus smaller islands? [Justify your answer in one or two sentences.] b) Would you predict Vp/Va to be larger or smaller on newly colonized islands that are closer to the mainland? [Justify your answer in one sentence.] 6. (12 points) You are considering the long-term effects of the ozone hole on the genetic health of a diploid plant population. In the following, consider a gene subject to recurrent mutation, where the deleterious mutations have selection coefficient, s, and dominance coefficient, h. [Support your answers with calculations. Do not use your answer to part a) in the other parts.] a) If more solar radiation enters through the atmosphere, the mutation rate at the gene might increase by a factor F to F . What is the new equilibrium frequency of heterozygous individuals carrying the deleterious mutation? b) Imagine that the deleterious mutation reduces the evaporative cooling ability of the plant. In this case, the selection coefficient, s, might increase by a factor C to C s. What is the new equilibrium frequency of heterozygous individuals? c) As in b), imagine that the deleterious mutation reduces the evaporative cooling ability of the plant, so that s increases by a factor C to C s. What is the new equilibrium mean fitness of the diploid population? Page 2 of 5 Evolutionary Genetics Midterm 2006 Name 7. (16 points) A group of researchers has developed a new breed of highly valuable black tulips. They produce a large number of bulbs from parents of known genotype for unveiling at the annual garden show. They expect all the flowers to be black, but when the flowers open, they discover that 6 of their 15,000 plants have even more valuable pale blue flowers. Upon returning to the nursery, they determine that their pale blue plants are heterozygotes for a white flower mutation (that is, BB individuals are black, Bb individuals are pale blue, and bb individuals are white). [Show calculations for parts a, b and d.] a) Based on these data, what is the mutation rate, µ from the black allele to the white allele ? b) The relative fitnesses of the three flower types are given by WBB = 1, WBb = 0.88, Wbb =0.76 Calculate the dominance coefficient h and the selection coefficient s for the white allele, b. c) Using the above fitnesses, is the white allele, b, dominant, partially dominant, additive, partially recessive or recessive to the black allele, B? d) If artificial selection practiced by the farmers increases the fitness of pale blue flowers by 50% (to WBb = 1.22), what would the equilibrium frequency of the black allele, B, be? [Show your calculations and ignore mutation for this part.] 8. (10 points) Barrett et al. (2006) maintained 200 lines of the haploid bacteria, Escherichia coli, for 10 days (110 generations). Each line started from a genetically identical stock and was maintained at a population size of 800,000. The authors then searched the evolved lines for signs that a beneficial sweep had occurred. Their method (using neutral markers) allowed them to detect Page 3 of 5 Evolutionary Genetics Midterm 2006 Name beneficial mutations that reached a frequency of 45% within this time frame. Assuming that a beneficial mutation started out at a frequency of 1/800,000, what is the minimum fitness advantage of a beneficial mutation that the authors could have detected? [Show your calculations.] 9. (15 points) A population of white-tailed deer that has existed on the small island of Vance is being relocated to the neighbouring island, Juniper, by wildlife managers. 45 deer are moved from Vance and added to the 78 deer already on Juniper. Genetic data show that these populations are genetically differentiated at two loci. The Vance population is fixed for alleles Spota and Tailb. The original Juniper population is fixed for the alternate alleles, Spotb and Taila . a) Estimate the amount of linkage disequilibrium in the new population immediately after the movement of adults from Vance to Juniper. [Support your answer with calculations.] b) If the rate of recombination between the two loci is 0.3, what formula predicts the level of linkage disequilibrium after one generation of recombination and what is the predicted value of D (assuming random mating and no selection)? c) In the absence of selection on either locus, do you expect the allele frequencies to change after one generation of recombination? Explain in one or two sentences why or why not. Page 4 of 5 Evolutionary Genetics Midterm 2006 Name 10. (12 points) A strain of mice was selected for decreased blood cholesterol levels. Over five generations, the mean blood cholesterol level of the mouse population decreased from 2.16 mg/ 100 ml to 2.01 mg/ 100 ml. The selection differential over this time period averaged 0.07 mg/ 100 ml per generation.[Support your answers with calculations.] a) What is the narrow sense heritability, h2, for blood cholesterol levels in this strain? b) If the phenotypic variance in the population at the start of the experiment is 8.35, what is the estimated additive genetic variance for blood cholesterol levels? c) After another 100 generations of selection using the same selection differential, the strain shows no further response to selection, and blood cholesterol levels plateau at around 1.92 mg/ 100 ml. In two sentences, explain what could account for this phenomenon and what might allow the population to respond to selection once again. 11. (10 points) Describe the principle introduced by Thomas Malthus and how Darwin used this principle to argue for evolution by natural selection. [Do not use more than the space below.] Page 5 of 5