11.16.07 - Darren Rothberg Biol 105 Evolution 11.16.07 I...

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Darren Rothberg Biol 105 – Evolution 11.16.07 I) M UTATIONS ! 1) Mutation a Ultimate source of all variation b Source of all evolutionary novelty c Without mutation, evolution would stop E. coli lines grown from single cells in a challenging medium Strain is incapable of recombination so only source of variation is mutation Both cell size and fitness changed over time (can freeze E. coli , store it and then thaw it thus can compete the same strain collected at different times!) d Rare: has little influence on changing allele frequencies in populations (i) Simply a source of novelty on which selection and drift can act e Occurs by chance alone 2) Point Mutation Genetic code is redundant: third position mutations less likely to be a problem than others a Effects (i) Creates a new allele (ii) Can affect phenotype Sickle cell trait (iii) Can be silent (neutral) b Base substitution (i) Caused by change errors during: Replication of DNA Repair of damaged DNA (ii) Significance: creates new alleles Silence mutation: no effect on phenotype; is still a new allele Missense: wrong amino acid can, but need not, affect phenotype: new allele Nonsense: early stop codon very likely to influence phenotype c Base addition or deletion (i) Insertions and deletions can cause serious reading frame shifts and nonsense (ii) Tend to be more serious than substitutions
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d Insertion of mobile elements (i) Can disrupt gene function (ii)
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