The Genetic Basis for Evolutionary Change I

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The Genetic Basis for Evolutionary Change I

• BIOL 100
• 17 November 2009

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Micro- vs. Macroevolution

• Microevolution is a change in a populations
  allele frequencies over time
• This lecture and the next
• Macroevolution is summation of microevolutionary
  changes over time
• Yields related species descended from common
  ancestors (phylogeny)
• Lecture on speciation

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Fig 16.8 p. 336

• Five Factors Promoting Microevolution
• 1) Natural selection
• 2) Genetic mutation
• 3) Genetic drift
• 4) Gene flow (dispersal)
• 5) Nonrandom mating

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Natural Selection

• Differences in survival and/or reproductive rates
  of the genetic variants of a species
• Traits selected for become more common in the
  population over generations
• Traits selected against become less common
• Mediated by environmental conditions
• Climate, sunlight, predators, competitors,
  resource availability, etc.

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Fig 16.14 p. 342

• Directional selection One phenotypic extreme is
  selected for, the other is selected against
• Very common

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Fig 16.14 p. 342

• Stabilizing selection Intermediate phenotypes
  are selected for, extremes are selected against

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Fig 16.14 p. 342

• Disruptive selection Both phenotypic extremes
  are selected for, while intermediates are
  selected against
• May be involved in new species formation

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Fig 16.11 p. 338

• Human-mediated directional selection in
  domesticated species

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The Peppered Moths of England

• Usually light gray dappled with black flecks
• All-black variant (generally very rare)
• Black variant became common near urban areas of
  England in late 1800s and early 1900s

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Kettlewells Experiment

• Released marked moths (peppered and black)
• Birmingham (industrial big city)
• Dorset (rural countryside)
• Results of recaptures
• Birmingham 21 recapture ratio of
  blackpeppered
• Dorset 21 recapture ratio of pepperedblack

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Fig 16.13 p. 340

• Hypothesized that bird predation and blending
  into background was the difference
• Confirmed via observation of predation on
  tethered moths