February_6_2013_NKW

February_6_2013_NKW - Ecol-335 6 February 2013(Monday...

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1 Ecol-335 6 February 2013 (Monday) Neutral Theory Reading: Futuyma Chapter 10 Test Friday, bring calculator Tonight at 7pm, Dr. Worobey on Infuenza evolution, Centennial Hall, - Neutral theory and nearly neutral theory Allele is effectively neutral if s < ~1/N e For population of 100, threshold is a ±tness differential of 0.01 For population of 1 million, threshold is a ±tness differential of 0.000001 Review on Nearly neutral A mutation that is effectively neutral in a small population may be governed by selection in a large population.
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2 What determines the relative roles of natural selection and genetic drift? Magnitude of s s = selective coefFcient (proportion by which Ftness is reduced or increased) in mutant Effective population size (N e ) Genetic Drift is main factor for N e s <1 Selection is important for N e s > 1 Affected by linkage of mutant allele to other chromosomal regions under selection ie, when does an allele behave as if neutral-- its fate depends mostly on chance rather than Ftness effects? Motoo Kimura Tomoko Ohta Neutral Theory Nearly Neutral Theory Most evolution at the molecular level is neutral with respect to Ftness. Population size does not affect the rate of neutral changes. Many changes are slightly deleterious & are Fxed by chance, despite negative selection. The rate of such changes is higher in small populations.
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3 l Selective Sieve z New Mutations Substitutions in lineage More effective with large N and large |s| Less effective with small N and small |s| Purifying selection is the most common (most mutations are deleterious)
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4 Distribution of selective coefficients of new mutations (?) Deleterious--------------neutral---------Beneficial ( s ) High frequency of slightly deleterious mutations Completely neutral mutations probably common Beneficial
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February_6_2013_NKW - Ecol-335 6 February 2013(Monday...

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