Deleterious effect on fitness beneficial after

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Unformatted text preview: VERN its fate. For a popula&on of Ne = 50 million s must be >10 ­8 for selec&on to govern its fate, so in large popula&ons selec&on dominates dri8. SO, in small popula7ons, SLIGHTLY deleterious muta7ons even though that have an effect on fitness, are governed by the forces of gene7c driP… Selective Sieve -- selection eliminates deleterious mutations New Mutations before selection: many deleterious mutations s 0! deleterious effect on fitness  beneficial after selection: few deleterious mutations Mutations fixed in lineage (= substitutions ) mostly neutral (or nearly neutral) s 0! deleterious effect on fitness  beneficial 6 Frequency of new mutations s 0! Selection Frequency of fixed mutations (=substitutions) s 0! Ne large-Even mildly deleterious mutations mostly purged s 0! Ne small-Many mildly deleterious mutations fixed Tomoko Ohta (1933Nearly Neutral Theory worked with Motoo Kimura Building on Kimura’s work: His protégé: Nearly Neutral Theory: Many new muta&ons are only slightly deleterious Their fate depends on popula&on size… Small popula&ons will undergo fixa&on of slightly deleterious muta&ons, which will accumulate over &me. 7 Average rates of subs7tu7on, in different genome regions •  Neutral Theory predicts that functionally important genome regions will evolve relatively slowly –  Many mutations are deleterious " •  these are eliminated, do not contribute to change –  Mutations in regions with little or no function will not be eliminated, resulting in fast evolution •  rate of change will depend on mutation rate –  Mutations in functionally important regions often will be eliminated, causing slow evolution Replacement changes (cause amino acid change) evolve slowest Silent/ synonymous changes evolve fast Pseudogenes (inac&vated genes) and intergenic spacers (non ­coding) evolve fast ...
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This note was uploaded on 02/02/2014 for the course ECOL 335 taught by Professor Reinthal during the Spring '10 term at Arizona.

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