Lect4-KR - Bacterial Genetics I PMB/MCB 112 September 3,...

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Bacterial Genetics I PMB/MCB 112 September 3, 2010
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Bacterial genetics Gene – segment of DNA that encodes a functional product, along with the regions that regulate its expression (product could be protein or RNA!!) Mutation – permanent, heritable alteration in the base sequence of DNA Allele – one of many alternative forms of a gene, wild-type allele vs. many possible mutant alleles Genotype = nucleotide sequence of the genome or gene in question Phenotype = visible or measurable property conferred by a particular genotype (wild-type or mutant)
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WT cells with normal phenotype X mutagenize cells Isolate X mutants Locate mutations in genome ( yfgA-Z) Infer that genes yfgA-Z are involved in generating normal phenotype X Genetic logic What genes cause this trait or phenotype?
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How do you isolate the mutants you want and identify the affected genes? Depends heavily on what phenotype you are studying! Selectable mutations confer a distinct advantage on the mutant strain under some environmental/growth conditions Examples: antibiotic resistance, bacteriophage resistance Nonselectable mutations may result in very clear, obvious changes, but they do not confer any growth advantage
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Examples of nonselectable mutants a) WT cells make their own histidine his mutants are His and require exogenous histidine mutants are histidine auxotrophs b) WT cells can use lactose as a source of carbon lac mutants are Lac and cannot grow if lactose is the sole carbon source in the medium c) WT cells swim and form diffuse colonies in semisolid agar Mot mutants cannot swim and form compact colonies d) WT cells are one color, mutants are another color
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Selection vs. Screen Selection : establish conditions where only the mutants you want will grow; parent strain and unrelated mutants die Examples: antibiotic resistance, bacteriophage resistance, particular temperature or nutrient source
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Lect4-KR - Bacterial Genetics I PMB/MCB 112 September 3,...

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