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Modern Evolutionary Biology: Population Genetics Overview

Explore the genetic structure of populations, the Hardy-Weinberg Equilibrium model, deviations from HWE like mutation, migration, and non-random mating, and factors influencing natural selection and fitness.

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Modern Evolutionary Biology: Population Genetics Overview

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  1. Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model D. Deviations From HWE:  1. Mutation 2. Migration 3. Non-Random Mating: 4. Populations of Finite Size and Sampling Error - "Genetic Drift" 5. Natural Selection: “differential reproductive success” we measure reproductive success as ‘fitness’ 1. Fitness Components:

  2. D. Deviations From HWE:  5. Natural Selection • Fitness Components: Fitness = The mean number of reproducing offspring / genotype - probability of surviving to reproductive age - number of offspring - probability that offspring survive to reproductive age

  3. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • Fitness = The mean number of reproducing offspring / genotype • - probability of surviving to reproductive age • - number of offspring • - probability that offspring survive to reproductive age • 2. Constraints: • i. finite energy budgets and necessary trade-offs:

  4. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • Fitness = The mean number of reproducing offspring / genotype • - probability of surviving to reproductive age • - number of offspring • - probability that offspring survive to reproductive age • 2. Constraints: • i. finite energy budgets and necessary trade-offs: GROWTH METABOLISM REPRODUCTION

  5. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • 2. Constraints: • finite energy budgets and necessary trade-offs: • TRADE OFF #1: Survival vs. Reproduction Maximize probability of survival Maximize reproduction GROWTH METABOLISM GROWTH METABOLISM REPRODUCTION REPRODUCTION

  6. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • 2. Constraints: • finite energy budgets and necessary trade-offs: • TRADE OFF #1: Survival vs. Reproduction • TRADE OFF #2: Lots of small offspring vs. few large offspring METABOLISM REPRODUCTION REPRODUCTION METABOLISM A few large, high prob of survival Lots of small, low prob of survival

  7. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • 2. Constraints: • finite energy budgets and necessary trade-offs: • Contradictory selective pressures: Photosynthetic potential Water Retention Leaf Size

  8. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • 2. Constraints: • finite energy budgets and necessary trade-offs: • Contradictory selective pressures: Rainforest understory – dark, wet Photosynthetic potential Water Retention Big leaves adaptive Leaf Size

  9. D. Deviations From HWE:  • 5. Natural Selection • Fitness Components: • 2. Constraints: • finite energy budgets and necessary trade-offs: • Contradictory selective pressures: Desert – sunny, dry Photosynthetic potential Water Retention Small leaves adaptive Leaf Size

  10. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: a. Calculating relative fitness Calculate relative fitness by dividing all fitness values by the LARGEST value.

  11. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: a. Calculating relative fitness b. Modeling Selection Multiply the initial genotypic frequency by relative fitness. Of course, not all organisms have survived, so these new frequencies do not sum to 1 any more.

  12. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: a. Calculating relative fitness b. Modeling Selection But we need to know what FRACTION of these SURVIVORS has each genotype. So, divide each frequency by the total. THESE are the genotypic frequencies in the survivors that have reached reproductive age and will breed.

  13. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: a. Calculating relative fitness b. Modeling Selection Calculate the gene frequencies, and compute genotypes in offspring (assuming all other HWE conditions are met, like random mating.)

  14. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: 4. Types of Selection

  15. D. Deviations From HWE:  5. Natural Selection • Fitness Components: • Constraints: • Modeling Selection: 4. Types of Selection Sexual Selection Some traits that decrease survival may be selected for because they have a direct and disproportional benefit on probability of mating. Intrasexual – competition within a sex for access to mates. Intersexual – mates are chosen by the opposite sex.

  16. Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model D. Deviations From HWE E. Summary; The Modern Synthetic Theory of Evolution Sources of Variation Agents of Change Mutation Natural Selection Recombination Genetic Drift - crossing over Migration - independent assortment Mutation Non-random Mating VARIATION

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