Natural Selection in Action

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Natural Selection in Action

• Ch.5, Sec.3

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• Natural Selection explains how populations change
  over many generations

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Generation Time

• Period between birth of one generation and birth
  of next

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Insecticide ResistanceHow does it occur?

• Step one application is made to a population
  where some individuals have resistant genes

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Resistant individuals reproduce pass on genes
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Next application no effect
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Adaptation to pollution

• PEPPERED MOTHS
• - before 1850s , pale moth common
• - after 1850, dark moth more common
• - pollution from industrial revolution blackened
  trees

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Speciation

• Formation of a new species from an original group
• 3 steps

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1) Separation

• Part of pop. Becomes isolated
• Sometimes by geographic barrier

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2) Adaptation

• Response to new environment
• Natural selection

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3) Division

• So different, cant interbreed
• Even with barrier removed

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