February_4_2013_NKW

Deleterious effect on fitness beneficial after

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

Ask a homework question - tutors are online