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section11_ak - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 11 Answer Key March 14-15, 2005 Bacterial Genetics—Complementation and Epistasis A. Understanding the basis Working in groups, choose the best answer to the questions below. Justify your choices. 1. A complementation test involves crossing a. wild-type organisms with recessive mutant variants. b. two different wild-type strains c. two strains displaying the same recessive mutant phenotype d. two strains displaying different recessive mutant phenotypes The goal of the test is to find out whether two mutations are in the same or different gene. The only way mutations can be in the same gene is if they display the same phenotype. It is a necessary, but not a sufficient condition. 2. Auxotrophy strains that ____complement____ each other will grow on minimal media. _do not complement_ In order to grow on minimal media, the new strain has to no longer display the mutant phenotype, i.e. the strains in the experiment have to complement each other. 3. A complementation test determines whether a. two pieces of DNA in the two strains interact with each other b. two pieces of DNA in the two strains are identical to each other c. products of expression of the gene(s) of interest in the two strains can interact d. products of expression of the gene(s) of interest in the two strains are variants of the same protein e. DNA from one strain interacts with the protein from the other On the underlying level, this is a variant of the gene regulation problem. The only way for a diploid to show mutant phenotype when two recessive mutants are considered, is if the mutations both disable the same protein. If no wild-type protein is available, there is no way to complete the pathway and display the wild-type phenotype. If the mutations disable different proteins, than, in a diploid, for each mutant protein, there is a wild-type copy available. That allows the wild-type copies to perform their function, complete the pathway, and allow the organism to display wild- type phenotype. 4. A complementation test a. determines the identity of the genes in a pathway. b. helps resolve the number of genes in a pathway. c. determines the epistatic order of genes in a metabolic pathway.
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