Evolution Among Populations

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Evolution Among Populations

• Chapter 16

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Evolution occurs on the Genetic Level

• Scientists combined Mendels work with Darwins
• Focused on how populations change (evolve)

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Because Members of a Population Interbreed They
Share a Common Gene Pool

• The combined genetic information of an entire
  population.

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Genetic Evolution

• Populations evolve (change) as gene pools change.

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Gene Pool Green genes, red genes, blue genes
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Variety is key to a populations ability to adapt

• Phenotypic variation (looks) is the result of
  genetic variation.
• So a bigger gene pool healthier population

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Two Main Sources of Genetic Variation

• Mutations- newly formed genes made by random
  changes in DNA
• Genetic Shuffling from sexual reproduction

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Natural Selection works to Change a Populations
Gene Pool

• Genes that produce adaptations become more
  common.
• This is known as directional selection.

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http//science.nhmccd.edu/biol/biolab/evolution1/e
volution1.htm
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Genetic Drift can lead to loss of Variation in
Small Populations

• Rare genes that can be preserved in large
  populations are lost in small ones

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Genetic Drift
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When populations get smaller, the gene pool gets
smaller

• Some genes are completely lost.
• This is known as the bottleneck effect.

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Bottleneck Effect

• Results is a loss in genetic variation.
• Ex. cheetahs

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Bottleneck Effect

• Even if a population recovers (increases in size)
  it will never be as healthy, because its genetic
  variation is lost
• Has less ability to adapt.

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If a population becomes segregated, it can evolve
into two separate species
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Speciation

• process by which a new species comes about
• Requires a portion of the population to become
  isolated.

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Isolating Mechanisms

• Geographic Isolation- population becomes
  seperated by geographic barriers

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Isolating Mechanisms

• Behavioral isolation groups develop different
  habits, mating rituals, etc.

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Isolating Mechanisms

• Temporal Isolation groups reproduce at
  different times

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Geographic Isolation
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Speciation Occurs when the two Groups can No
Longer Interbreed

• Isolation means the two groups dont share genes
• As a result traits become increasingly different