exam4_notes - Chapter 16Dissection of Gene Function...

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Chapter 16 Dissection of Gene Function (11-18-05) Problems (1, 7, 18, 19, 21) Germinal Mutation A mutation in gamete-forming tissue. An individual with the “new” germinal mutation will not show the phenotype but the mutation can be transmitted to progeny. Somatic Mutation A mutation in any non-gamete producing tissue. The individual with the “new” somatic mutation may exhibit a mutant phenotype but the mutation can't be transmitted to progeny. Conditional Mutation The allele only expresses the mutant phenotype under certain environmental conditions. (e.g., ts t emperature s ensitive) The protein product functions at the permissive temperature but is non-functional at the restrictive (non-permissive) temperature. Auxotrophic Mutation The individual must be supplied with certain nutrients (amino acids, nucleotides, vitamins). Commonly used when studying microorganisms. WT is prototrophic (nutritionally self-sufficient). Resistance Mutation Confers the ability to grow in the presence of an inhibitor. (e.g., antibiotic or virus/phage) Antibiotic resistance mutations can arise from a mutation in the gene encoding the target of the drug or a mutation in the gene encoding a transporter of the drug. Human Genetics Germinal mutations are detected by the sudden appearance of the abnormal phenotype in a pedigree with no previous record of abnormality. Dominant mutations are relatively easy to detect. Recessive mutations can go unnoticed for several generations. X-linked recessive mutations are easier to detect than autosomal.
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Mutant Hunts Experiments designed to isolate mutants that affect a specific biological function. Genetic Selections Techniques designed to separate rare mutant individuals from WT. Need a selectable phenotype. Only the appropriate mutants survive. Genetic Screens Strategies designed to identify desired mutant individuals (mutant phenotype) from a large number of individuals. (Figure 16-4) Mutagens Used to increase mutation rates. (e.g., chemicals or UV radiation) Forward Genetics Analyzing heritable mutant phenotypes at the genetic level before performing molecular analyses of the isolated mutants. Requires methods to identify the mutant genes (e.g., gene mapping) Reverse Genetics This approach starts with a WT molecule (typically a cloned gene or a purified protein). The WT gene is then mutated to identify the mutant phenotype. Single Cell Haploid Organisms-Bacteria and Fungi (advantages) 1) Grow as single cells in liquid culture or as colonies. 2) Easy to examine millions of individuals. 3) Isolated single cells generate a clonal population (colony) of genetically identical cells. 4) Mutants are easily identified (dominant or recessive).
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I. Forward Genetic Selections A. Detection of Reverse Mutations (auxotroph prototroph) 1) Grow mutant culture in minimal medium + supplement. 2)
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exam4_notes - Chapter 16Dissection of Gene Function...

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