LECTURE4B - L e c t u r e 4 b : F o r w a r d G e n e t ic...

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Lecture 4b: Forward Genetic Analysis Readings : Ch 2 pp 31-33, 57-61; Ch 4 pp 163-64; Gentic Suppression Forward vs reverse genetics Genetic dissection Mutagens Genetic analysis of mutants Dominant or recessive? Number genes affected? Number of genes identified How do the genes interact? Gene mapping
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Gene interactions and modified Mendelian ratios: Suppression
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Gene interactions and modified Mendelian ratios: Suppression
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Gene interactions and modified Mendelian ratios: Suppression
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Gene interactions and modified Mendelian ratios: Suppression
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Penetrance and expressivity contrasted
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Variable expressivity
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Incomplete penetrance and pedigrees
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Genetic Dissection How does “this” work? about how it works Investigation of a biological process using mutants Genetic screens “Mutant hunt” Look through natural or mutagenized population to identify mutants unable to perform process of interest Some types of screen: • Morphological, Behavioral, Biochemical
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Mutagens used to increase frequency of finding chemical mutagens – e.g. ethylmethane sulfonate (EMS) point mutations -- affect proteins through truncation or “loss” of key amino acids radiation – e.g. X-rays, fast neutrons leads to small or large deletions of DNA or even chromosome insertional mutagens mutagenize genes by sticking a large chunk of DNA in the middle of it or its regulatory sequences e.g. transposable elements, T-DNA in plant inserted DNA acts as a “tag” to identify the gene involved Gene T-DNA
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Selection Only the desired mutants survive Easy to screen large numbers Limited to specific types of genes/roles Screening Analyze individuals Give greater range of phenotypes Allow to identify unexpected phenotypes More work than selection Screening can be easy or laborious Genetic screens – selection vs screening Fig 16-4
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Genetic screens - selection Auxotrophic mutants of fungi Fig 16-6 min +adenine min +leucine minimal media min +adenine +leucine
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Genetic screens Cell cycle (
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LECTURE4B - L e c t u r e 4 b : F o r w a r d G e n e t ic...

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