Are there natural selection advantages for being friends with certain types of people?AGENTS OF EVOLUTIONNATURAL SELECTIONPowerPoint PresentationDifferential survivalDifferential fecunditySlide 7Slide 8Slide 9A1A1 A1A2 A2A2Slide 11Slide 12E. Change in allele frequency due to selectionSlide 14Slide 15B. Outcome is determined by fitness differencesSlide 17Slide 18Selection in natural populationsSlide 20Slide 21Natural Selection on Coat Color in Pocket MiceSlide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Are there natural selection advantages for being friends with certain types of people? Associating with people with similar ethnic/cultural backgrounds aids cooperative efforts (fitness advantage) Geography and environment favor “likes” to associate. Avoidance of the unfamiliar- (“birds of a feather flock together” Third parties or social environment selection promote similar people to interactAGENTS OF EVOLUTIONI. Deviations from Hardy-Weinberg EquilibriumA. Determining which force of evolution1. particular properties of populations or phenotypes can be used to infer evolutionary force2. Mutation, Migration, Genetic Drift and Inbreeding, Natural Selection and Sexual SelectionNATURAL SELECTIONI. Understanding Selection and FitnessA. What is natural selection?1. Non-random differential proliferation of phenotypes within a generation-non-random: change is DIRECTED with respect to the phenotype-differential proliferation: certain phenotypes are MORE LIKELY to survive and reproduce than others-operates on PHENOTYPES--not genotypes-natural selection occurs WITHIN a generation-ONLY RESLTS IN EVOLUTION IF FAVORED PHENOTYPE IS HERITABLEB. Measuring Natural Selection1. Fitness is the currency of natural selection (How we measure natural selection value of trait)Absolute fitness = WProbability of survival X reproductive outputDifferential survivalv = viability= Probability of individual survival (zygote --> adult)genotype viability A1 A1 v11 A1 A2 v12 A2 A2 v22Differential fecunditym = fertility= number of gametes released per individualgenotype fertility A1 A1 m11 A1 A2 m12 A2 A2 m22Absolute fitnessW = v . m = viability x fertilitygenotype absolute fitness A1 A1 W11 = v11 m11 A1 A2 W12 = v12 m12 A2 A2 W22 = v22 m22Relative fitness = wAbsolute fitness of a phenotype Absolute fitness of “most fit” phenotypeSelection coefficient = s= 1 - wA measure of the strength of selection against a phenotypeRanges from 0 (most fit phenotype) to 1.0 (least fit phenotype)2. Example: Plant populationA1A1 A1A2 A2A2Prob. of survival 0.90 0.85 0.80Number of seeds 3.0 3.0 5.0Calculate W, w, sExample: Population of plants MAKE THIS AN OVERHEADA1A1 A1A2 A2A2Prob. of Survival 0.90 0.85 0.80Number of seeds 3.0 3.0 5.0Absolute Fitness (W) (.9)(3) (.85)(3) (.8)(3)=2.7 =2.55 =4.0Relative fitness (w) 2.7/4 2.55/4 4/4=.68 =.64 =1Selection Coefficient 1-.68 1-.64 1-1=.32 .36 =0Selection will favor the phenotype of A2A2, thus frequency of A2 should increase in next generationA1A1 A1A2 A2A2Absolute fitness W 2.7 2.55 4.0Relative fitness w 0.68 0.64 1.0Selection coeff. s 0.32 0.36 0.0Selection will favor the A2A2 phenotype and the frequency of A2 will increaseAt genetic equilibrium (HWE) A2 will be fixed (q = 1.0) and A1 will go extinct (p = 0)Evolution at this locus will stop unless mutation or migration introduces a new allele with higher fitness than A2This type of selection is directional.C. Predicting genotype frequencies with selectionA1A1 A1A2 A2A2Rel. freq. before select. p22pq q2Relative fitness w11w12w22Selection coefficient 1-w11=s111-w12=s121-w22=s22Rel. freq. After select. p2w112pqw12q2w22 w w ww= p2 w11 + 2pq w12 + q2 w22 = mean fitness of populationD. Allele frequencies after selection1. Relative frequency of A1 after selection2. Relative frequency of A2 after selectionp´ = p2 w11 + pq w12 wq´ = q2 w22 + pq w12 wE. Change in allele frequency due to selection1. ∆p = change in frequency of A1 allele in response to natural selection ∆q = change in frequency of A2 allele in response to natural selection∆p = (pw11 + qw12 - w )∆q = (qw22 + pw12 - w ) p w q wIf ∆p = 0 then locus is in HWE and no evolution is occurring. If ∆p > 0 then the relative frequency of A1 is increasing. A1 is favored. If ∆p < 0 then the relative frequency of A1 is decreasing. A2 is favored.III. Outcomes of Natural SelectionA. What happens to pt eventually?pttB. Outcome is determined by fitness differences1. Fitness of all genotypes is equal W11 = W12 = W22 Any allele frequency is an equilibrium (HWE) t0pt01for any p0 , pt = p02. Directional selection for A1A1-A1A1 homozygote has highest fitnessW11 > W12 > W22 t0pt01p = 1 no A2 pt1Equilibrium (HWE) is reached when p = 1.0^t0pt01pt0A1 lostA2 fixedqt1Equilibrium (HWE) is reached when p = 0.03. Directional selection for A2A2-A2A2 homozygote has highest fitnessW11 < W12 < W22^Selection in natural populations1. ADH (alcohol dehydrogenase) in DrosophilaHOalcohol aldehydeR C OHHR CHADHTwo alleles in DrosophilaADHF fasterADHS slowerdegrades ethanolSelection experimentWhere did the ADHF alleles come from?Natural Selection on Coat Color in Pocket MiceMc1rDD or Mc1rDd = blackMc1rdd = agoutiHoekstra & Nachman 2003Hoekstra et al. 2004In lava flow populations:W11 > w12 > w22In sandy soil populations:W22 > w12 > w11W11 < W12 > W22 t0pt01p^equilibriumstableptp^4. Overdominance-A1A2 heterozygote has highest fitnessBoth alleles, A1 and A2, will remain segregating in the populationHeterozygotes are resistant to typhoid fever bacteriumS. typhi selects for overdominance at ∆F508 geneW11 < w12 > w22The selective advantage of crypsis in mice. Vignieri et al. 20105. Underdominance-BOTH homozygotes have HIGHER fitness than heterozygote t0pt01p^equilibriumunstablept0 or 1W11 > W12 < W22Both alleles, A1 and A2, will only remain segregating in the population if initial frequency is p = 0.5 and q = 0.5 AND W11 = W22W22 > w11 >