14_lecture - Chapter 14 Mechanisms of Genetic Variation 1...

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Unformatted text preview: Chapter 14 Mechanisms of Genetic Variation 1 stable, heritable changes in sequence of bases in DNA ◦ point mutations most common from alteration of single pairs of nucleotide from the addition or deletion of nucleotide pairs ◦ larger mutations are less common insertions, deletions, inversions, duplication, and translocations of nucleotide sequences mutations can be spontaneous or induced 2 Mutations: Their Chemical Basis and Effects arise without exposure to external agents may result from errors in DNA replication ◦ due to base tautomerization resulting in transition and transversion mutations ◦ due to insertion or deletion of nucleotides may also result from the action of mobile genetic elements such as transposons 3 Spontaneous Mutations 4 Figure 14.1 5 Figure 14.2 caused by agents that directly damage DNA ◦ base analogs structurally similar to normal bases mistakes occur when they are incorporated into growing polynucleotide chain ◦ DNA modifying agents alter a base causing it to mispair ◦ intercalating agents distort DNA to induce single nucleotide pair insertions and deletions 6 Induced Mutations 7 Table 14.1 8 Figure 14.4 wild type ◦ most prevalent form of gene forward mutation ◦ wild type fi mutant form reversion mutation ◦ mutant phenotype fi wild type phenotype suppressor mutation occurs when the second mutation is at a different site than the original mutation 9 Effects of Mutations 10 Table 14.2 point mutations ◦ in protein-coding genes can affect protein structure in a variety of ways are named according to if and how they change the encoded protein the most common types are: silent, missense, nonsense, and frameshift mutations 11 Mutations in Protein Coding Genes silent mutation – change nucleoside sequence of codon – but not the encoded amino acid missense mutation – a single base substitution that changes codon for one amino acid into codon for another amino acid nonsense mutation – converts a sense codon to a stop codon frameshift mutation – results from insertion or deletion of one or two base pairs in the coding region of the gene 12 Point Mutations conditional mutations ◦ expressed only under certain environmental conditions auxotrophic mutant ◦ unable to make an essential macromolecule such an amino acid or nucleotide has a conditional phenotype wild-type strain from which it arose is called a prototroph 13 Other Types of Mutations mutations in Regulatory Sequences ◦ conditional lac operon mutants many of these mutations map in the operator site and...
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This note was uploaded on 02/04/2012 for the course BIO 326R taught by Professor Whiteley during the Spring '08 term at University of Texas at Austin.

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14_lecture - Chapter 14 Mechanisms of Genetic Variation 1...

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