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Pop gen

Population Genetics

(Evolution 2)

  1.  Individuals do not evolve; populations do
  2. Natural selection operates on phenotype and therefore favors or selects genotypes – natural selection alters gene frequencies
  3. Gene Pool
    1. All the genes that occur in a population
    2. The occurrence of any particular gene
  4. Allele frequency = proportion of different gene forms
  5. Evolution is a change in allele frequency within a population
  1. Natural selection does not cause genetic change in individuals
  2. Natural selection works on individuals, but evolution only affects populations
  3. Evolution is a change in allele frequencies due to differential reproduction – Fitness is measured by reproductive success
  4. Evolutionary changes are not “good” or “progressive”
  1. Source of variability = mutation and recombination of alleles during reproduction
  1. Mutations occur 1 in 10,000 to 1 in 1,000,000
  2. Provides potential
  3. Not goal-directed
  1. Equilibrium population – Hardy & Weinberg
  1. Does not change = genetic equilibrium
    1. No mutation
    2. No gene flow
    3. Population must be very large (infinite)
    4. All mating must be random
    5. No natural selection
  2. Equation – sum of all allele frequencies must be 1

P2 + 2pq + q2 = 1

  1. Migration
  1. Immigration = new members coming into population
  2. Emigration = moving out
  1. Genetic Drift
  1. Random change in allele frequency especially in smaller populations
    1. Reduces genetic variability in a small population
    2. Increases variability between populations
  2. Population bottleneck – larger population reduced to a small one, which then recovers to a larger number
  3. Founder Effect – bottleneck that alters gene frequency
  4. Nene example
  1. Sexual selection, harem breeding, assortative mating (select mates that are similar to self)
  1. Natural selection is not about survival, but about reproduction – differential reproduction (individuals with certain alleles leave more offspring than others)
  2. Selection
    1. Directional (favors one extreme of trait distribution – shift left or right
    2. Stabilizing (selects for average)
    3. Disruptive (selects for both extremes)
  3. Coevolution
  4. Forces that influence
    1. Competition
    2. Predation
    3. Symbiosis
    4. Sexual selection
    5. Kin selection/altruism
  5. Extinction – complete and total death of a species – mostly due to habitat destruction