Mechanisms of MicroevolutionMicroevolution vs. MacroevolutionThe Population is the Basic Unit of Microevolutionary ChangePopulation GeneticsSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Evolutionary Change is a Consequence of Changes in Allele FrequenciesEvolution as Change in Allele/Genotype FrequencyThe Hardy-Weinberg EquilibriumAssumptions of the Hardy-Weinberg EquillibriumSlide 17Slide 18Slide 19Slide 20These apply under Hardy-Weinberg equilibrium:Slide 22Question:Answer.Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31The Mechanisms of EvolutionMutationSlide 34Some types of mutations.Cat MutationsSongbird mutationsSlide 38Slide 39Mutations are the ultimate source of genetic variationExample-an interesting mutation:Genetic DriftEffects of Genetic DriftSlide 44Founder EffectSlide 46BottlenecksSlide 48Slide 49The Neutral Theory of Molecular Evolution.Slide 51Slide 52Slide 53Population StructureAllele Flow:Effects of Allele FlowAllele Flow v.s. Genetic DriftSlide 58Allele flow and selectionNonrandom MatingInbreedingSlide 62Assortative MatingExamples of assortative mating in humansNatural SelectionSlide 66Slide 67What is Fitness?Slide 69Absolute fitness vs. relative fitness.Relative FitnessExampleAnswerSlide 74Directional SelectionSlide 76Example of Directional Selection: The peppered moth, Biston bettulariaSlide 78Slide 79Slide 80Stabilizing SelectionSlide 82Examples of Stabilizing SelectionExample of Balancing Selection, and of the Differing fitness of an Allele in Different Environments: Sickle Cell Anemia in HumansSlide 85Slide 86Disruptive or Diversifying SelectionFrequency-Dependent SelectionSlide 89Slide 90Slide 91The Environment affects the Fitness of AllelesSlide 93Selection is weak against rare recessive allelesMutation-Selection BalanceSlide 96Slide 97Slide 98Slide 99Slide 100The Comparative MethodThe Comparitive Approach is Good for Making Inferences About Evolutionary Trends.Slide 103Slide 104Criticisms of Optimality ModelsEcological Game TheoryExample of an Ecological “Game”, Stealing in Digger WaspsSlide 108Slide 109Slide 110Slide 111Slide 112Slide 113Kin SelectionSlide 115Slide 116Hamilton’s RuleSlide 118Example; multiple foundresses in Polistes.Slide 120Slide 121Slide 122Slide 123Slide 124Slide 125Slide 126Example-tunicates recognize each other by chemical signals (MHC genes, the same chemicals that enable our bodies to reject foreign organs) on their skin. Kin colonies of tunicates grow together. Non-kin colonies form a “zone of death” between each other.Mechanisms of MicroevolutionReading:Freeman, Chapter 24, 25Microevolution vs. MacroevolutionThe term “microevolution” applies to evolutionary change within a lineage–It occurs continuously.–Depending upon the organism and the circumstances, it can transform a lineage. dramatically over time.–Alternately, a lineage may appear to remain the same over time-this is called stasis.Macroevolution is the origin and extinction of lineages.–It can happen gradually, or slowly.Both processes are essential to evolution. Microevolution is probably better understood, and better documented, because in some organisms it takes place on timescales we can study directly by experiment and direct observation.Ironically, in “On the Origin of Species” Darwin lays out a theory of microevolution…he assumed macroevolution would inevitably result from microevolution.–It would be 100 years later that Ernst Mayr, and others, would develop a scientific theory of speciation.–The replacement of one species by another (as opposed to the replacement of one allele by another), by the way, is an ecological process..it is not evolution in the usual sense, though this phenomenon usually leads to extinction of some species and diversification of others.The Population is the Basic Unit of Microevolutionary ChangeThe genotype of an individual is, essentially, fixed at birth.The population is the smallest unit where evolutionary change is possible.–Unlike individuals, populations permit the origin of new alleles through mutation, and the change in the frequency of alleles through selection, genetic drift, etc..Individuals do not evolve, populations and species evolve.Population GeneticsPopulation genetics refers to the study of evolution via the observation and modeling of allele frequencies and genetic change in populations of organisms. There are three parameters to keep in mind: –allele frequency: the proportion of a specific allele at a given locus, considering that the population may contain from one to many alleles at that locus. –genotype frequency: the proportion of a specific genotype at a given locus, considering that many different genotypes may be possible.–phenotype frequency: the proportion of individuals in a population that exhibit a given phenotype.Consider a population of N organisms.Two phenotpyes, yellow and tan. Suppose that they are diploid and reproduce sexually. Consider one gene with two alleles, A and a. The possible genotypes are therefore:AA, Aa, and aa.Phenotype Frequencies To calculate the frequency of a phenotype, count the number of individuals with that phenotype, and divide by the total. Therefore, the frequency of the yellow phenotype in the population below is 4/10=.40Genotype Frequencies-To calculate the frequency of a genotype in the population, find the total number of individuals in the population with that genotype, and divide by the population size, N.–f(AA)= #(AA)/N–f(Aa)= #(Aa)/N–f(aa)= #(aa)/NQuestion: What are the frequencies of the AA and Aa, and aa genotypes in the population below?AaAAAAAaAaAaaaaaaaaaAnswer: freq(AA)=2/10=.20 freq(Aa)=4/10=.40 freq(aa)=4/10=.40AaAAAAAaAaAaaaaaaaaaAllele Frequencies-–By convention, the frequency of the dominant allele is called p, thus the frequency of the recessive allele, q=1-p.To calculate the frequency of an allele in the population, add the total number of homozygotes for that allele to half the heterozygotes, and divide by the population size, N.–p= ((#AA) + (1/2)(#Aa))/N–q= ((#aa) + (1/2)(#Aa))/NIf you already know the genotype frequencies,–p=f(AA)+(1/2)f(Aa)–q=f(aa)+(1/2)f(Aa)Question: What are the frequencies of the A and a alleles in the population below? AaAAAAAaAaAaaaaaaaaaAnswer: freq(A)=p=(4+(2x2))/20=.40 freq(a)=q=(4)+(4x2)/20=.60 or q=1-.4 since p+q=1AaAAAAAaAaAaaaaaaaaaEvolutionary