Chapter 15 Mutation, Recombination, and Repair

Chapter 15 Mutation, Recombination, and Repair - Mutation,...

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Mutation, Recombination, and Repair Suggested problems: #1, 2, 3, 4, 8, 10, 11, 13, 14, 16, 19, 20, 23, 24, 25, 29
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Where does genetic variation come from? 1.Mutation 2.Recombination
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Consequences of point mutations within genes
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Transition: purine purine pyrimidine pyrimidine Transversion: purine pyrimidine pyrimidine purine
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Consequences of point mutations within genes
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Other places mutations can have phenotypic consequences: 1. Mutations that affect splicing. 1. Mutations that affect promoter or regulatory regions. 1. Mutations that affect chromatin neighborhood (insulators, rearrangements to heterochromatic regions.
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Southern blot: detect the presence of specific sequences by probing
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Probes can be used to detect specific macromolecules Southern blot: detect DNA Northern blot: detect mRNA Western blot: detect protein (here, rather than base complementarity, an antibody that recognizes the protein is used as probe)
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Consequences of point mutations on gene products
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How does mutation occur? 1. Spontaneous mutation a. spontaneous lesions b. errors in DNA replication 1. Mutagens a. base replacement b. base alteration c. base damage d. X-rays e. transposable elements
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Spontaneous lesions in DNA Depurination : -Loss of purine base -A mammalian cell undergoes depurination 10,000 times in a 20hr mitotic cycle! -These are repaired, but sometimes the repair results in a point mutation Deamination : -deaminated cytosine is uracil (unrepaired uracil will pair with adenine, thereby leading to a transition) -methylcytosine (of epigenetically silenced chromatin) deaminates to thymidine. Oxidative damage to bases: -thymidine glycol blocks DNA replication unless repaired - alternative guanosine form mispairs with thymidine
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Errors in DNA replication Alternative forms of bases, called tautomers, are found very rarely (bases can shift between the two forms) Keto form is the normal base Imino and enol forms are found rarely Tautomeric shift only leads to transitions pyrimidine pyrimidine purine purine
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Tautomeric shifts in DNA bases may cause mutations Errors in DNA replication
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Errors in DNA replication: insertions and deletions caused by replication slippage in highly repetetive regions
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Replication slippage mutations cause trinucleotide repeat diseases in humans increases in the number of three base nucleotide repeats results in disease states ie, (CGG) 6-59 = normal (CGG) >200 = diseased “premutations” in parents, with intermediate repeat numbers, make the repeats more unstable and frequently lead to disease states in their progeny ie, (CGG) 60-200
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How does slippage result in diseases? Example 1: Fragile X mental retardation syndrome
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This note was uploaded on 05/28/2011 for the course BIO 220 taught by Professor Dr.leatherman during the Spring '10 term at N. Colorado.

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Chapter 15 Mutation, Recombination, and Repair - Mutation,...

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