Sample_Macroevolution__Qs_S'10_KEY - PRACTICE STUDY...

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1 PRACTICE STUDY PROBLEMS ON MACROEVOLUTION - Phylogenetics & Speciation KEY 1. Oil content in corn kernels is a quantitative trait, varying from <2% to >8%. Assume this trait is determined by many genes (the exact number does not matter) each with two alleles, one for “ high oil” and the other for low oil.” On the graph, draw a dotted ( ----- ) line to show the expected phenotypic distribution in a population where seeds with low oil content failed to provide enough nutrition for seedlings to grow and seeds with high oil content were preferentially eaten by birds. 2. The graph below shows the distribution of beak sizes in a population of medium ground finches in the Galapagos. a) If the island on which they are living is subsequently successfully colonized by a different finch species from a neighboring island whose bill size ranges from 9-11 mm, predict what you would expect to happen to beak size in the medium ground finches, and why. Draw your expected result on the blank graph on the right. (bimodal curve, with means of the two peaks at larger and smaller beak sizes than mean of original curv.) The arrival of the second finch species would likely result in disruptive selection b/c the two species would be competing most strongly for the same sized seeds. Individuals with beaks larger or smaller than the original, most common (mean) beak size would experience less competition, and if these individuals thus had higher fitness, then the original bell-shaped curve of beak sizes would take on a bimodal distribution with peaks higher and lower than the original mean. b) Is this event likely to result in speciation? If you say yes, explain why and how speciation would occur. If you say no, explain why not, including what condition would have to be met. This example of disruptive selection could be a first step toward speciation b/c the population is splitting into two groups based on the morphological character bill length. However, for speciation to occur, the two groups would also have to become reproductively isolated, as could happen if they were to start mating assortatively (short-beak birds only with other short beak-beak birds, same for long-beaked) so there was no gene flow between them and traits that resulted in pre-zygotic isolation evolved to help keep them separate.
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2 3. Duke Forest is home to two similar species of coral root orchid. One, “early coral root,” blooms in the spring. The other, “autumn coral root,” blooms in late summer and fall. a) Although the two species very closely resemble each other morphologically and both live in the same wooded habitat, why are they regarded as separate species according to the Biological Species Concept? They are reproductively isolated
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Sample_Macroevolution__Qs_S'10_KEY - PRACTICE STUDY...

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