Chapter 11 Lecture Notes

Chapter 11 Lecture Notes - Mutation: The Source of Genetic...

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Unformatted text preview: Mutation: The Source of Genetic Variation Chapter 11 Mutations Mutation = Can be: Spontaneous errors in DNA replication Induced exposure to radiation, chemicals, viruses, or mutagenic agents Detecting Original Mutations Dominant mutations easiest to detect via pedigree analysis Xlinked mutations are... examination of male progeny Autosomal recessive difficult to identify original mutant An Xlinked Mutation: Hemophilia Heterozygous carrier Fig. 11.2 Spontaneous Mutation Rates Mutations are rare 1 error per 1,000,000 copies of a human gene Rates of Mutation Mutations don't often affect populations: Redundancy genetic code Recessive mutations don't affect heterozygotes Mutants = fewer children Lower reproductive success early death Mutation rate = Rates of Mutation To measure this the mutant phenotype must: Not be recessive alleles Fully expressed Have clear paternity Gene based only Caused by one gene Differences in Mutation Rates Factors that influence mutation rates: Size of gene Nucleotide sequence nucleotide repeats Spontaneous chemical change Genes rich in G/C pairs Worse for big or small genes? Environmental Factors: Radiation Fig. 11.5 Radiation Exposure Radiation can damage DNA Formation of molecules that mutate DNA Repair is possible Too many mutations = cell death or cancer Chernobyl, April 1986 An estimated increase of 14,000 cancer deaths Fig. 11.4 Effect of Chemicals Mutations caused by chemicals: Base analog Chemical modification of nucleotide Chemicals that bind to DNA alter DNA shape = deletion or addition Base Analog Fig. 11.6 Fig. 11.6 Chemical Modification Fig. 11.7 Chemicals that Bind to DNA Intercalating agents = Can cause a deletion or insertion Breakdown products of common pesticides Acridine Orange Fig. 11.8 Point Mutations Point mutation = Point mutations can: Have no effect Change one amino acid for another = missense mutation Point Mutations Point mutations can: Change stop codon to aa codon = Sense mutation Longer or shorter proteins AA codon becomes stop codon = Nonsense mutation Shortens the protein Missense Mutations in Hemoglobin Fig. 11.9 Population Genetics: Sickle Cell Genes Why is there a high frequency of individuals heterozygous for sickle cell anemia in West Africa? Malaria! Frameshift Mutations Insertion or deletion of nucleotides Reading frame is altered THE MAN CAN RUN Insertions Change the Reading Frame Fig. 11.11 Trinucleotide Repeats Occur in triplet repeats i.e. CAG or GAA CAGCAGCAGCAGCAG Triplets increase in number Cause many diseases Known as allelic expansion Trinucleotide Repeat Diseases Fragile X Syndrome causes mental retardation Caused by expansion of FMR gene 1% of institutionalized males Why? Affects males more than females Allelic Expansion in the FMR 1 Gene at the Fragile X Locus Fig. 11.13 Trinucleotide Repeat Diseases Heterozygous females normal Males with <230 copies transmitter males Daughters of transmitter males = high risk of affected sons Inheritance of FragileX syndrome Transmitter male Unaffected females Affected males Fig. 11.12 Mutations with Expanded Trinucleotide Repeats Anticipation = Gene Expansion and Anticipation More repeats = earlier onset of disease DNA Repair Systems DNA can be repaired Repair systems are genetically they can mutate Common damage Thymine (T) dimers UV Light May Produce Thymine Dimers Fig. 11.15 Repair Rates From table 11.4 Thymine Dimer repair 50,000/hour Single stranded breaks 2,300/hour Breaks due to radiation 0.001/hour DNA Repair Systems Very complex many genes Damage to repair systems = cancer EX: Xeroderma pigmentosum exposure to sunlight 1/250,000 Repair System Disorders 1000X increase in cancer risk Mutations in at least 8 different genes Fig. 11.16 Cystic fibrosis >1300 mutations in CFTR Phenotype & Mutation position in Gene gene Large range of phenotypes Mutations = substitutions, deletions, frameshift mutations Mutations in Cystic Fibrosis Gene Fig. 11.17 Genomic Imprinting Genomic Imprinting = Genes marked during: gamete formation or early embryonic development Genomic Imprinting Mechanism is not clearly understood Does not affect all genes Not a mutation modification of the DNA affects the gene expression ...
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This note was uploaded on 04/04/2008 for the course BIOL 105C taught by Professor Drake during the Fall '07 term at Saginaw Valley.

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