PS8_Key - BICD100 Genetics Fall 2005 Reinagel PROBLEM SET 8...

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BICD100 Genetics Fall 2005 Reinagel PROBLEM SET 8 FORWARD GENETICS (Lecture Nov 8) 1) In bacteriaphage λ you are studying three mutations that cause plaques to be either speckled, blue, or diffuse. You cross a speckled, blue, diffuse strain to wild type λ by co-infection (all bacteria are infected with both phages). You plate the resulting lysate and analyze the phenotypes of the plaques caused by the progeny phage: Phenotype Number of Plaques Speckled, blue, diffuse 2121 Speckled, blue 3 Speckled, diffuse 344 Blue, diffuse 21 Speckled 22 Blue 349 Diffuse 4 Wild type 2136 Derive the most accurate map you can of the order of these genes and the distances between them, indicating any ambiguities. Phenotype Number of plaques s-d d-b s-b speckled, blue, diffuse 2121 PT PT PT speckled, blue 3 DCO (rare) NP NP PT speckled, diffuse 344 PT NP NP blue, diffuse 21 NP PT NP speckled 22 NP PT NP blue 349 PT NP NP diffuse 4 DCO (rare) NP NP PT wild type 2136 PT PT PT 5000 total 2 valid ways to solve: either use rare class to infer which is in the middle, as shown, or solve all three pairwise distances and then infer the best linear map. diffuse in middle (rare DCO class) s-d distance = 3+21+22+4 x 100 = 1 cM 5000 d-b distance = 3+344+349+4 x 100 = 14 cM 5000
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BICD100 Genetics Fall 2005 Reinagel s-b distance (not required if you already have the map order) = 344+21+22+349 x 100 = 14.7 cM 5000 answer: s d b --|-------|----------|------- 1 14 You were not asked to determine interference (if you did, you’re a pro). There are no ambiguities (unresolvable positions) because the rare DCO class verifies the relative positions of the two genes that are very close. NOTE that this is not a tetrad, so the tetrad equations do not apply
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BICD100 Genetics Fall 2005 Reinagel 2) You isolate a new bacterial species E. oilspillcleani that is able to break down crude oil into carbon dioxide and water. Tests show that your wild type strain can break down decane, eicosane, naphthalene, phenanthrene, and pyrene, and it is naturally tolerant to high temperature conditions (temp R ). You isolate a temperature sensitive variant of the wild type parent, and separately
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PS8_Key - BICD100 Genetics Fall 2005 Reinagel PROBLEM SET 8...

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