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Transcript
Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female b. Components of fitness: Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female b. Components of fitness - probability of female surviving to reproductive age Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female b. Components of fitness - probability of female surviving to reproductive age - number of offspring the female produces Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female b. Components of fitness - probability of female surviving to reproductive age - number of offspring the female produces - probability that offspring survive to reproductive age Deviations from HWE I. Mutation II. Migration III. Non-Random Mating IV. Genetic Drift - Sampling Error V. Selection 1. Measuring “fitness” – differential reproductive success a. The mean number of reproducing offspring (or females)/female b. Components of fitness - probability of female surviving to reproductive age - number of offspring the female produces - probability that offspring survive to reproductive age c. With a limited energy budget, selection cannot maximize all three components… there will necessarily be TRADE-OFFS. 5. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 5. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets GROWTH METABOLISM REPRODUCTION 5. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets Maximize probability of survival Maximize reproduction GROWTH GROWTH METABOLISM REPRODUCTION METABOLISM REPRODUCTION 5. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets Trade-offs within reproduction REPRODUCTION METABOLISM REPRODUCTION METABOLISM Lots of small, low prob of survival A few large, high prob of survival 5. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 5. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness (ω) 1 1 0.25 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness (ω) 1 1 0.25 Survival to Reproduction 0.16 0.48 0.09 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness 1 1 0.25 Survival to Reproduction 0.16 0.48 0.09 = 1.00 = 0.73 This = “mean fitness of the population” (ω) 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness 1 1 0.25 Survival to Reproduction 0.16 0.48 0.09 = 0.73 Geno. Freq., breeders 0.22 0.66 0.12 = 1.00 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness 1 1 0.25 Survival to Reproduction 0.16 0.48 0.09 = 0.73 Geno. Freq., breeders 0.22 0.66 0.12 = 1.00 Gene Freq's, gene pool p = 0.55 q = 0.45 = 1.00 3. Modeling Selection Selection for a Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.8 0.2 Relative Fitness 1 1 0.25 Survival to Reproduction 0.16 0.48 0.09 = 0.73 Geno. Freq., breeders 0.22 0.66 0.12 = 1.00 Gene Freq's, gene pool p = 0.55 Genotypes, F1 0.3025 = 1.00 q = 0.45 0.495 0.2025 = 100 3. Modeling Selection Selection for a Dominant Allele Δp declines with each generation. 3. Modeling Selection Selection for a Dominant Allele Δp declines with each generation. BECAUSE: as q declines, a greater proportion of q alleles are present in heterozygotes (and invisible to selection). As q declines, q2 declines more rapidly... 3. Modeling Selection Selection for a Dominant Allele Δp declines with each generation. So, in large populations, it is hard for selection to completely eliminate a deleterious allele.... 3. Modeling Selection Selection for a Dominant Allele Δp declines with each generation. Also, this means that in different populations with different gene frequencies, the rate at which p changes will vary (even though the relative fitness differences are the same) 3. Modeling Selection Selection for a Dominant Allele Δp declines with each generation. Rate of change also depends on the strength of selection; the difference in reproductive success among genotypes. 3. Modeling Selection Selection for a Dominant Allele Selection for an Incompletely Dominant Allele Selection for an Incompletely Dominant Allele p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.4 0.2 Relative Fitness 1 0.5 0.25 Survival to Reproduction 0.16 0.24 0.09 = 0.49 Geno. Freq., breeders 0.33 0..50 0.17 = 1.00 Gene Freq's, gene pool p = 0.58 Genotypes, F1 0.34 = 1.00 q = 0.42 0.48 0.18 = 100 Selection for an Incompletely Dominant Allele - deleterious alleles can no longer hide in the heterozygote; its presence always causes a reduction in fitness, and so it can be eliminated from a population. In this case, the beneficial allele is said to have an ‘additive’ effect, because one dose is ‘good’ but two doses in the homozygote is ‘better’. Heterosis - selection for the heterozygote p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.4 0.8 0.2 Relative Fitness 0.5 (1-s) 1 0.25 (1-t) Survival to Reproduction 0.08 0.48 0.09 = 0.65 Geno. Freq., breeders 0.12 0.74 0.14 = 1.00 Gene Freq's, gene pool p = 0.49 Genotypes, F1 0.24 q = 0.51 0.50 0.26 Maintains both genes in the gene pool peq = t/s+t = 0.75/1.25 = 0.6 AA = 1.00 Aa aa = 100 Maintains both genes in the gene pool peq = t/s+t = 0.75/1.25 = 0.6 Heterosis - selection for the heterozygote Sickle cell caused by a SNP of valine for glutamic acid at the 6th position in the beta globin protein in hemoglobin (147 amino acids long). NN NS SS The malarial parasite (Plasmodium falciparum) cannot complete development in red blood cells with this hemoglobin, because O2 levels are too low in these cells. Selection Against the Heterozygote p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.4 0.6 Relative Fitness 1 0.5 0.75 Corrected Fitness 1 + 0.5 1.0 1 + 0.25 formulae 1+s 1+t = 1.00 Selection Against the Heterozygote - peq = t/(s + t) p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.4 0.6 Relative Fitness 1 0.5 0.75 Corrected Fitness 1 + 0.5 1.0 1 + 0.25 formulae 1+s 1+t = 1.00 Selection Against the Heterozygote - peq = t/(s + t) - here = .25/(.50 + .25) = .33 p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.4 0.6 Relative Fitness 1 0.5 0.75 Corrected Fitness 1 + 0.5 1.0 1 + 0.25 formulae 1+s 1+t = 1.00 Selection Against the Heterozygote - peq = t/(s + t) - here = .25/(.50 + .25) = .33 - if p > 0.33, then it will keep increasing to fixation. p = 0.4, q = 0.6 AA Aa aa Parental "zygotes" 0.16 0.48 0.36 prob. of survival (fitness) 0.8 0.4 0.6 Relative Fitness 1 0.5 0.75 Corrected Fitness 1 + 0.5 1.0 1 + 0.25 formulae 1+s 1+t = 1.00 Selection Against the Heterozygote - peq = t/(s + t) - here = .25/(.50 + .25) = .33 - if p > 0.33, then it will keep increasing to fixation. - However, if p < 0.33, then p will decline to zero... AND THERE WILL BE FIXATION FOR A SUBOPTIMAL ALLELE....'a'... !! UNSTABLE EQUILIBRIUM!!!! E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection E. Selection 4. Types of Selection - Directional E. Selection 4. Types of Selection - Directional E. Selection 4. Types of Selection - Stabilizing E. Selection 4. Types of Selection - Disruptive Lab experiment – “bidirectional selection” – create two lines by directionally selecting for extremes. Populations are ‘isolated’ and don’t reproduce. E. Selection 4. Types of Selection - Disruptive African Fire-Bellied Seed Crackers E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Frequency-Dependent Selection The selective value depends on the frequency of the allele/phenotype in the population. “rare mate phenomenon” = negative frequency dependence Elderflower orchids: - don’t produce nectar - bumblebees visit most common flower color and get discouraged, try the other color…. Back and forth. - visit equal NUMBERS of the two colors, but that means that a greater proportion of the rarer flower color is visited. As phenotype gets rare, fitness increases. Maintains alleles in population (of yellow flowers) - Morphs of Heliconius melpomene and H. erato Mullerian complex between two distasteful species... positive frequency dependence in both populations to look like the most abundant morph in a given area E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Interactive Effects E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Interactive Effects - antagonistic pleiotropy Pleiotropy Ester1 allele: confers resistance to insecticide, but increases risk of predation. Increased in frequency along coast of France, where spraying occurred (benefit > cost) Did not increase inland much (did increase due to migration), as cost > benefit and selected against Ester1 was eventually replaced by the Ester4 allele, which conferred a weaker benefit for pesticide resistance BUT had no negative effects inland… so the net benefit was greater. E. Selection 5. Interactive Effects - mutation-selection balance A deleterious allele (selectively disadvantageous) can be maintained in a population by mutation: Δq = m – sq2 = rate they are added by mutation – rate lost by selection against the homozygous genotype. qeq = √m/s E. Selection 5. Interactive Effects - mutation-selection balance - selection and drift Deterministic Effects of Selection > Random Effects of Drift At small sizes, it is possible to lose an adaptive allele. However, just by chance, adaptive alleles can become fixed – rapidly increasing the reproductive success of population