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presentation_11_12 - Lecture 11 cont d Mutation rates Rates...

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1 Lecture 11 cont±d Mutation rates • Rates vary among genes, chromosome regions (mutational “hotspots”). • Rates depend on environmental factors (mutagens). • Higher mutation rates may be advantageous under certain circumstances (rapidly changing environment).
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2 Mutation as an evolutionary force • What direct impact does recurrent mutation have on allele frequencies in populations? • Mutation rates ( μ )are often low. • Therefore, recurrent mutation is a very weak evolutionary force (acting alone, takes very long time to alter allele frequencies). • BUT…Mutation is the ultimate source of new variation.
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3 Phenotypic consequences of mutations • Dominant and recessive refer to effect of an allele on phenotype when that allele is paired with a second allele in heterozygous condition. • Example: “loss of function” alleles are often recessive. A 1 A 2 = A 1 A 1 : A 1 is dominant to A 2 A 1 A 2 = A 2 A 2 : A 1 is recessive to A 2 A 1 A 2 intermediate between A 1 A 1 and A 2 A 2 : incomplete dominance In diploid organisms, phenotype depends on interaction between two alleles New variants (alleles) may be – Advantageous — will go to Fxation (freq of allele = 1) in the population, replacing old allele. – deleterious — eliminated by natural selection (freq of allele = 0). – effectively “neutral” — no influence on phenotype. ±itness consequences of mutation
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4 Cumulative frequency distributions of the effects of new mutations on Ftness distadvantageous advantageous A gene affects multiple phenotypic characters ==> characters do not evolve independently.
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This note was uploaded on 09/28/2008 for the course BIOEE 2780 taught by Professor Geber during the Fall '07 term at Cornell.

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presentation_11_12 - Lecture 11 cont d Mutation rates Rates...

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