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Organic Evolution

Mid-term 2018


BIOL 4417/5517: Organic Evolution Fall 2018

Due Friday October 12, 2018 at 5:00 PM

Mid-Term Exam This is a take-home exam: use your text, notes and other materials to prepare your answers. You may discuss questions with classmates but must write your answers independently. Although factual, accurate answers are expected, much of your grade will depend upon the thoughtfulness and creativity of your answers. Concise, complete & grammatically correct sentences are essential; references are allowed but not required. Please number your answers using the question numbers (otherwise, your grader will get confused). The exam is due Friday October 12 at 5:00 PM, submitted on the Moodle website. Part 1. The following problems require quick calculations and short answers (a couple of sen- tences). Solve BOTH of the problems. 5 points each. Read each question carefully.

1. Due to the small population size, the coat color in Yellowstone National Park’s gray wolves (Canis lupus) is largely determined at the K-locus by the alleles A1 and A2. Yellowstone wolves with genotype A1A1 have the black coat beneficial for hunting in forested ecosystems; fitness of W11 = 0.80. Wolves with the genotype A2A2 have the gray coat normally found in open tundra ecosystems; W22 = 0.75. Wolves A1A2 are interme- diate for coat color; W12 = 1.0. At equilibrium, what will be the frequencies of the A1 allele and the three genotypes? Show all work and fully justify your answer.

2. At another wolf locus, wild-type individuals have genotype T1T1 and very white teeth. Now consider an an- cient mutation that introduced a neutral allele, T2: individuals with T1T2 have somewhat less white teeth and those with T2T2 have substantially less white teeth. Although initially only found in one individual, after 100 generations T2 increased to a frequency of q = 0.01. After 500 generations, q = 0.1. Today, after 1000 generations, q = 0.55. What is the probability today that the neutral T2 will eventually become fixed in the population? Show all work and justify your answer.

Part 2. The following questions require concise answers, about 1 paragraph. Answer only FOUR of the questions. Read the questions carefully. 15 points each. 3. A small group of vampire ground finches (Geospiza septentrionalis) were flying between islands in the Ga-

lapagos and on their way to a Halloween party. A storm blew in and redirected the birds to an island that had never previously been inhabited by vampire ground finches. After a few years, the birds have happily made the new island their home and they are visited by an ornithologist. The ornithologist bands the finch- es, collects feathers for a genetic analysis, and finds that this isolated population of vampire ground finches is not in Hardy-Weinberg equilibrium. Why is this, and what is the potential long-term significance?

4. It has been said, “Natural selection does not work as an engineer works. It works like a tinkerer.” What might this mean? In what ways is natural selection more like a tinkerer than a biological engineer?

5. Southern red-backed voles (Myodes gapperi) are a small rodent native to most of Canada and south into our local Mink Creek area. The red-backed voles get their name from the red/brown streak of fur that can extend from the nape of their neck to their rump. The length of the red/brown streak has a strong genetic component (1 gene, 2 alleles). These voles prefer to live in forests and don’t like to leave the forest or travel between forests. Jonathan has been conducting small mammal trapping in Mink Creek and (amazingly!) has captured every single southern red-backed vole in the area. Jonathan has counted 502 voles with very long streaks (probably homozygous for allele 1), 601 voles with mid-length streaks (probably heterozy- gotes), and 397 voles with small streaks (probably homozygous for allele 2). Is the population in Hardy- Weinberg equilibrium? If not, offer a hypothesis for why it might be out of HWE, and briefly justify your hypothesis. Does the population survey data support your hypothesis?

6. Since it is not possible for evolutionary biologists to go back in time, phylogenetic relationships are hypoth- esized and described in phylogenetic trees. Briefly describe one of the approaches used to infer phylogeny. What types of criteria are used for that approach? How can the suitability a tree be evaluated?

7. When a beneficial mutation occurs in an individual (e.g. from A1 to A2), what proportion of the population has the mutated allele (A2)? What are the potential fates of the mutated allele? What might be the conse- quences for a population with this mutation?



BIOL 4417/5517: Organic Evolution Fall 2018

Due Friday October 12, 2018 at 5:00 PM

8. The evolution of antibacterial resistance frequently involves a resistance allele that initially exists in the population at very low frequencies even though that allele is slightly deleterious under normal conditions (when no antibiotics are present). What processes might work to maintain the deleterious allele in the bac- terial population under those conditions? How does this process maintain the deleterious allele in the population?

Part 3. The following question requires a more extensive answer, about 1 page. Provide exam- ples to illustrate your points and define all your terms. 30 points.

9. The Russian olive (Elaeagnus angustifolia) was introduced to central and western North America in the late 1800’s as an ornamental tree and a windbreak. The trees soon escaped cultivation and began reproduc- ing into the wild. Since then, Russian olive has become invasive, displaced countless native cottonwood for- ests (Populus sp.), and become naturalized across the western US. Studies of population genetics show that Russian olive populations in North America are NOT in Hardy-Weinberg equilibrium. What does this mean? Propose two hypotheses that explain HW disequilibrium in Russian olive and describe the ra- tionale for both hypotheses. Briefly outline a possible test for one of those hypotheses.

Part 4. Extra credit (up to 5 points each!). Each question requires concise answers (a couple of sentences). Read each question carefully. 10. The average mutation rate across the human genome is 4.8×10-9 per base pair per generation. Statistically,

each humane zygote should have 317 mutations. Why don’t we observe more humans with obvious muta- tions in society? What types of mutations do we most commonly observe?

11. The root of the phylogeny of primates represents the common ancestor to all primates (see cladogram, Fig. 19.4 in your text, p. 681). Based only on this tree, which primate species has changed most (in genotype, phenotype, or both) since diverging from this common ancestor?

a. Lemur b. Chimpanzee c. Both primate lineages have experienced the same amount of change d. It is not possible to determine an answer from this tree

Choose the best answer from the 4 possibilities and justify your answer. 12. If humans evolved from great apes, why are there still great apes? Explain.

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