Bio Lab Wksht & HW Questions 20

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15 C-2. MacClade Using the computer program, MacClade 3.1, you will work in pairs to construct a most parsimonious tree depicting the phylogeny of cartoon cladisticules above. Your final task will be to construct a phylogenetic tree using the data set of characters for vertebrates on the desktop of your computer. In phylogenetics, parsimony relates to the number of times a character changes from one state to another. A parsimonious tree will be the tree with the fewest number of changes (=steps). Ideally, we are also looking for a tree with character changes appearing only once. This is a statistic called consistency index (=CI). A CI of 1.0 is more parsimonious than a tree with a CI of 0.35. Watch for these numbers in the lower right hand corner of your computer screen. Your lab instructor will step you through the operation of the MacClade program. Please do not randomly click on icons or get ahead of your instructor – it is easy to get ‘lost’ in this exercise.
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Unformatted text preview: 1. Open the file called “Cladisticules”. Note your starting tree length and CI. Starting tree length _______ steps. Starting CI __________. To manipulate your tree, click on a branch and drag it to a new branch. Try to group taxa that show shared derived characters. By doing this, you are attempting to uncover monophyletic groups that are made up of an ancestral species and all of its descendents (Fig 25-10, p. 498). Your tree length should go down and the CI should go up as you approach the most parsimonious tree for this data set. Final tree length _______ steps. Final CI __________. Draw your final tree in the space below. Indicate the evolutionary changes on the branches by placing the character number below the group in which it appears. Do any characters appear more than once on your tree? If yes, which one/ones?...
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