IDENTIFYING MUTANTS - A mutant that now requires a specific...

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IDENTIFYING MUTANTS   Mutants can be detected by selecting or testing for altered phenotype. Even when a mutagen is  involved, the number of mutants represents only a very small percentage of the population.     1. Positive (direct) selection---cells are placed in surroundings where only mutants can grow.  For example, if the mutation is resistance to penicillin, the bacteria can be placed in a growth  medium containing penicillin, and only mutants can grow.     2. Negative (indirect) selection---this is looking for a cell that has LOST the ability to perform  a certain function due to a mutation. The technique used is called replica plating. 
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Unformatted text preview: A mutant that now requires a specific growth factor that previously could be synthesized is called an auxotroph. IDENTIFYING CHEMICAL CARCINOGENS Carcinogens are mutagens that cause cancer. One way of identifying these is the Ames test. The chemical being tested is added to medium containing mutant bacteria. If the chemical is mutagenic, it will cause more than a random number of mutants to revert to their original form (back-mutations or reversions). The more of these, the more powerful the mutagen. About 90% of the chemicals that are positive on this test will be carcinogens....
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