1 x 103 nt disite 4 2 x 108 nt changessite 13750

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Unformatted text preview: chimps and humans? divergence &me=? human ? Mya 1.2% chimp Use: t = D/2u t= t= 0.012 substitutions/site 2*0.001 substitutions/site/million years 6 million years! NEUTRAL THEORY 10 Measures of varia7on can be used to calculate popula7on size Long ­term Ne in human is es&mated to be ~10,000 to 20,000. As of today, the human popula&on is es&mated by the US Census Bureau to be 7, 064,088,716 humans Why the discrepancy? Reflects small popula&on size during recent human history 1 million years ago to the origin of human agriculture about 10,000 years ago. 11 Using polymorphism to measure Ne in humans (effective population size over time) Nucleotide diversity can be used to measure population variation In humans, average silent site heterozygosity is 0.0011 differences per site. Mutation rate is 2 x 10-8 changes per site per generation. What is the effective population size (Ne)? π  = 4Neµ Ne = π /4µ =( 1.1 x 10 ­3 nt diff/site) / (4)( 2 x 10 ­8 nt changes/site) = 13,750 •  Nucleotide diversity (π) π  is the pairwise divergence between two alleles or the proportion of nucleotide sites at which two alleles randomly drawn from the population differ Why so small? " (Current census population size is 7 Billion about 500,000 times greater) 12 Three equations to know from Neutral Theory Measuring nucleotide diversity in great apes 1. What is the mean time to fixation for a new NEUTRAL mutation? t = 4Ne generations (diploids) also = coalescence time (how far back for all modern copies to trace to a single ancestral copy) 2. What is the rate of molecular evolution? (what is the rate of substitution of mutations in a population)? K = µ changes/genome region/unit time (units are same for K and µ) 3. What is the relationship between population size and variation? π = 4Neµ Bonobo π = 0.001 Chimps π = 0.002 Gorilla...
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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 University of Arizona- Tucson.

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