Lecture 19 - Homologous Recombination The physical exchange...

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Homologous Recombination The physical exchange of DNA between distinct molecules Prokaryotes – serves mainly as DNA repair system. Can occur during conjugation and phage infection. Eukaryotes – genetic mixing occurs primarily during meiosis. Also occurs through DNA repair.
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Homologous Recombination
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The Holliday Model First Proposed by Robin Holliday: Genet. Res. Camb. 5: 282-304. 1964 Saccharomyces cerevisiae and Ustilago maydis
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Homology means identical > 100 bp.
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DNA strands are nicked in the same location Strands then exchange
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Sometimes call a chi form since it resembles χ And Ligate to form a Holiday Structure.
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Branch migration can occur in either direction for many base pairs. Correction of both heteroduplexes to the same allele = Gene Conversion
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Double Stand Break Model for Homologous Recombination
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How Do we Infer Gene Function from a Mutant Phenotype? A little Bedtime story……
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Once upon a time there was a gene. Her name was Rugosus (Latin for wrinkled). She made a protein called: Starch branching enzyme I
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SBE job was to make long branched sugars within the seed. These Sugars held on to water tightly!
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Then one day, there was a mutation! X No Rugosus mRNA was made! No SBE I was made! The UnBranched Starch didn’t Hold water inside the cells! The Pea seed Wrinkled like a Raisin in the sun! X
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The mutant rugosus was very sad. That only one of the pair of rugosus genes was passed on from each parent. That the next generation had one maternal and one paternal copy of rugosus. He showed that the mutant rugosus was part of a gene pair Until one day a curious monk appeared!
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Rugosus became famous as the first gene shown to segregate, And she showed that long branched sugars are required for maintaining water balance in mature pea seeds, and she lived happily ever after! The End
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So you have a mutant was does that mean? 1) Amorph – loss-of-function or null mutation 1) Hypomorph – reduction of function 1) Antimorph – dominant negative, poisons subunits 1) Hypermorph – gain-of-function, to much activity 1)
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