Evolution%20of%20Populations - PowerPoint PPT Presentation

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Evolution%20of%20Populations

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Evolution of Populations Evolution as Genetic Change Natural Selection on Single Gene Traits Natural selection never acts on genes, always on the whole organism But ... – PowerPoint PPT presentation

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Title: Evolution%20of%20Populations


1
Evolution of Populations
  • Evolution as Genetic Change

2
Natural Selection on Single Gene Traits
  • Natural selection never acts on genes, always on
    the whole organism
  • But, if that organism produce a gene change that
    affects survival, natural selection will act
    differently on that organism because of that gene
    change.
  • Ex Lizard color
  • Brown vs. Black
  • Change the survival, change the gene pool

3
Distribution of Phenotypes in Polygenic Traits
  • When many genes affect one trait, you get many
    phenotypes
  • The graph to the right shows the number of
    individuals (area under the curve) for the
    different phenotypes

4
Natural Selection on Polygenic Traits
  • Directional Selection when individuals at one
    end of the curve have higher fitness than
    individuals in the middle or at the other
    end-Thus the curve will shift left or right
  • ExBeak Shape

5
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6
Natural Selection on Polygenic Traits
  • Stabilizing Selectionwhen individuals near the
    center of the curve have higher fitness than the
    others-Thus the curve will get narrow and tall
  • -Survival favors the average
  • Ex Birth weight in humans

7
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8
Natural Selection on Polygenic Traits
  • Disruptive Selectionwhen individuals at opposite
    ends of the curve have higher fitness-Thus causes
    the curve to dip in the middle
  • -Average struggle to
  • survive
  • Ex Bird Beaks

9
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10
Genetic Drift
  • In small populations, individuals that carry a
    particular allele may leave more descendants than
    others, just by chance
  • Over time, this can cause a change in phenotype
    from the original population
  • Ex Founders Effect occurs when a small
    population settles in a location separate from
    the rest of the population.
  • Ex Amish

11
Ex Bottleneck
12
Genetic EquilibriumNo Evolution/Change
  • Hardy-Weinberg Principle allele frequencies
    remain the same if
  • Random Mating Occurs
  • Large Population
  • No immigration or emigration
  • No mutations
  • No natural selection
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