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Published byHilary Crawford Modified over 9 years ago
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Estimating genetic diversity ( within populations = a function of the number of polymorphic sites in a population (S) “Watterson’s theta” Allele 1: ACTGGCTGAACTT Allele 2: ACTGGTTGAACTT Allele 3: GCTGGTTGAACCT * * * S=3 n = number of alleles
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A second estimate of 4N Allele 1: ACTGGCTGAACTT Allele 2: ACTGGTTGAACTT Allele 3: GCTGGTTGAACCT k = number of differences between pairs of alleles i and j n = number of alleles
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Testing neutrality Tajima’s D statistic proportional to: Under neutrality, Tajima’s D ≈ 0
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Under directional selection, Tajima’s D < 0 Testing neutrality
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1. Gene trees don’t always match the species tree 2. Gene divergence often precedes population divergence Gene tree Species tree T/4N e 2N e Two rules of gene trees near the species boundary
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30 gene trees from Australian finches Jennings & Edwards (2005) Evolution 59, 2033-2047. P. acuticaudaP. heckiP. cincta
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Gene flow erodes population monophyly Migration event reconstructed by parsimony
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Counting the number of interpopulation coalescent events
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s as an index of divergence time
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s as an index of gene flow
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Gene flow erodes population monophyly
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Genetic differentiation between populations or b, between populations; w, within populations
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Identifying outlier loci using Fst
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Identifying loci under pollution-driven selection using Fst and outlier loci
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Distribution of F st among loci in humans
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Gene tree monophyly as an indicator of natural selection European corn borer
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Faster approach to concordance for mtDNA versus nuclear DNA
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Different behavior of nuclear and organelle genes ParameterNuclearorganelle: uniparental, haploid (e.g., mtDNA, cpDNA or Y chromosome) Comments Effective population sizeNeNe N eo = 1/4N e When sex ratios are 1:1 Chance of fixation in a local populationlowerhigher" " " Founder effectmildstrong Depth of gene tree (in generations)deepshallowT = 4N e Genetic diversitymoderatehighdiversity = 4N e µ Time to reciprocal monophyly of lineages in sister populations longshortT = 4N e, N eo F st -- geographic variationlowhighmigration rates of sexes equal Concordance between gene and species trees lowerhigherdepends on length of phase of incomplete isolation of populations;
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Examples of discordance between gene and species trees
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Examples of large mtDNA breaks within species
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Snow geese: widespread distribution of two divergent mtDNA clades Snow goose
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Structured populations of hyperthermophilic Archaea
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past present Genetic diversity ( ) or population size Signatures of stable and expanding populations Long internal branches Short external branches Short internal branches Long external branches Stable population Expanding population
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Holarctic songbirds Star phylogenies in holarctic species
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