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Answer key 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 B C D E F A 1 3 5 7 4 B 2 6 6 3 C 7 5 1 D 2 7 E 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 a dot 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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