Lect 11: Inbreeding, evolution at multiple loci. Exam 1, Monday, 2 October. Consequences of Inbreeding: Genotype frequencies

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1 Lect 11: Inreeding, evolution t multiple loci Exm 1, Mondy, 2 Octoer Non-rndom mting-- Inreeding evolutionry consequences Synthesis: drift-migrtion: popultion structure Popultion genetics of pririe chickens Evolution t multiple loci Linkge disequilirium Selection, selective sweeps Lectures 1-10, plus first prt of tody Ls week 2-5 Redings Ch 1-6 On the we pge Lecture notes Study guide Consequences of Inreeding: Genotype frequencies Fr() = p 2 + pqf Fr() = 2pq - 2pqF Selfing F = 0.5 Consequences of Inreeding: Genotype frequencies Fr() = p 2 + pqf Fr() = 2pq - 2pqF F = 0 p 2 2pq F = 1 p 0 Inreeding leds to deficiency of heterozygotes nd n excess of homozygotes Inreeding does not ffect llele frequencies q 2 q Evolutionry Consequences of Inreeding? Inreeding depression Evolutionry Consequences of Inreeding? Inreeding depression! = 1 - w s /w o w s = fitness of selfer w o = fitness of outcrosser Dudsh 1990 Sti ngulris! = 1 - w s /w o Field:! = /0.66! = 0.62

2 Evolutionry Consequences of Inreeding? In Humns: Fig 6.28 Fig Cuses of Inreeding depression? Fr() = p 2 + pqf Fr() = 2pq - 2pqF Incresed homozygosity Decresed heterozygosity Inreeding importnt when: selection on rre recessive lleles s homozygotes: unmsked overdominnce Synthesis: -Migrtion Popultions drift to different llele frequencies H within pops decreses F st increses: divergence in llele frequencies mong popultions F ST Time

3 Migrtion Migrtion Strong gene flow F st? H w/in pops? Smller Lrger -migrtion low gene flow Synthesis: Greter Pririe Chickens F ST high gene flow 25,000 2,000 Figure Time Opposite effect on H Why decline despite more hitt? Why reound? Figure 6.3 Greter Pririe Chickens

4 Extinction vortex, genetic rescue Decline: Smll popultions, drift, sence of migrtion, inreeding depression Evolution t multiple loci Fitness ffected y more thn one genetic locus? Two loci:, Mny loci: Quntittive genetics (polygenic inheritnce) Two loci, two lleles Reound: Migrtion restored polymorphism, reduces inreeding Prent Gmetes Linkge Equilirium Definition: Rndom ssocition of lleles t different loci Definition: Non-rndom ssocition of lleles t different loci Gene pool Locus 1 (fr = p) (fr = q) (fr = ps) (fr = pt) Wht if selection fvors llele? Pro. tht llele ssocited with = s Gene pool Locus 1 (fr = p) (fr = q) (fr! ps) (fr! pt) Wht if selection fvors llele? Pro. tht llele ssocited with! s Locus 2 (fr = s) (fr = t) (fr = qs) (fr = qt) Pro. tht llele ssocited with = s No effect on llele Locus 2 (fr = s) (fr = t) (fr! qs) (fr! qt) Selection on llele cuses chnge in frequency of llele Coefficient of linkge disequilirium (D) Wht elimintes it? (fr = g ) (fr = g ) (fr = g ) (fr = g ) D = g g - g g D rnges to 0.25 D = 0 Linkge equilirium When D! 0, non-rndom ssocitions Recomintion reduces D over time* D = D(1 - r) r = recomintion rte *IF no force cts to mintin D genertion r = 0.0 r = 0.1 r =

5 Wht cretes it? Wht cretes it? 1. Selection 2. Genetic drift 1. Selection on oth loci Locus 1: color Locus 2: Hitt choice 3. Pop n dmixture 4. Non-rndom mting GG, Gg rr codpted gene complex RR, Rr gg Survivors will tend to hve g nd r lleles Wht cretes it? 2. Selective sweeps: hitch-hiking y closely linked llele Positive selection ( only) Selective Sweeps : gmetes more common thn y chnce Positive selection ( only) hitchhikes to high frequency Review Disequilirium creted y selection, drift, dmixture & non-rndom mting Disequilirium roken down y recomintion (unless mintined y selection, etc.) When D! 0, selection on one locus cuses evolutionry chnge t nother Inreeding (Non-rndom mting) increses homozygosity, decreses heterozygosity ffect evolution through inreeding depression Synthesis: Unmsking deleterious recessives The sence of heterozygotes under overdominnce -migrtion: outcome for polymorphism within popultions nd divergence etween popultions depends on the reltive strength of these two forces Forces cting on Greter Pririe Chicken: strong drift, inreeding depression, wek migrtion. Evolutionry consequences reversed with migrtion Evolution t two loci: linkge disequilirium cused y selection, selective sweeps