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key Answer to Worksheet #1 Phylogenetic Tree 1. Using the records from the first table, a data matrix, record the number of differences between pairs of organisms A B C D E B 1 C 3 2 D 5 6 7 E 7 6 5 2 F 4 3 1 7 5 2. Currently living organisms (or, most recent organisms) will be placed at the top of the tree. For this example, all of them are alive so list A through E in one line. 3. Coming down the tree, we are moving into the past. The last common ancestor of the organisms will be shown on the very bottom of the tree. How to Create the Tree: 1. Start by finding the closest relatives The pair or pairs of organisms that have the FEWEST differences between them In this example, beetles A and B have only ONE difference, so they are the closest relatives C and F also have just one difference so they are the closest relatives as well Mark dot a under A and B, showing the separation of evolutionary lines leading to the contemporary forms of A and B Repeat this for C and F 2. Find organisms that have more than one difference B differs from C by TWO features, so the last common ancestor of this pair lived before the common ancestor of A and B and C and F Organisms D and E also differ by just two features o They may be closely related to each other, however, not to the other organisms o Therefore, D and E are paired up by linking them with a common ancestor 3. See which organisms differ by three or four characteristics To confirm the earlier assumption of the relationship between A, B, C and F 4. Next, look for organisms that differ by FIVE features These are beetles A and D, C and E, and E and F When these groups are linked by a common ancestor, the tree is complete ... View Full Document

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