Answers to pg' 325

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Answers to pg. 325

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1 List 5 conditions that disrupt genetic
equilibrium and cause evolution.

• 1. Genetic Drift
• A change in a gene pool due to chance.
• Two Examples
• A. Bottleneck Effect- caused by Natural
  disasters.
• Cheetahs popn as low as 10,000.

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Causes of Evolution

• Genetic Drift
• B. Founder Effect
• When a small population breaks away from a larger
  one to colonize a new area. Their allele
  frequencies can be different.
• Amish of Lancaster, Penn. - Polydactyl

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Causes of Evolution

• 2. Gene Flow
• The movement of Alleles into or out of a
  population.
• Caused by immigration and emmigration.

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Causes of Evolution

• 3. Mutations
• Changes in the genetic material and are the raw
  material for evolutionary change.

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Causes of Evolution

• 4. Nonrandom Mating
• Individuals choose their mates for specific
  reasons.
• Selection serves to eliminate the less-fit
  individuals.
• Inbreeding
• Sexual selection

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Causes of Evolution

• 5. Natural Selection
• Those individuals who are better adapted in a
  particular environment exhibit better
  reproductive success.

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3 Contrast gene flow with genetic drift.

• gene flow is genes moving around populations
  because of reproduction, while genetic drift is
  change in allele frequencies because of random
  events like volcanoes killing all the plants on
  the side of a mountain.

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4 Why is genetic drift more significant in
small populations

• The gene pool is much smaller so alleles may
  disappear in a short time due to chance.
• Ex rare orchid variety gets eaten by herbivore
  all of its unique genes are lost.

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5 Contrast types of selection

• Directional selection -when one phenotype is
  favored at one of the extremes of the normal
  distribution.
• Think- bell shaped curve.
• Ex roseate spoonbill

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• Stabilizing selection- organisms with extreme
  traits are selected against Examples
  camoflage- organisms too bright or dark get
  eliminated more often

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• Disruptive selection- favoring of both extremes
  and selects against the common trait.
• Example-finch bird beaks

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6 Why might a harmful allele persist in a
population for many generations?

• If the heterozygous condition is not selected
  against the trait will be passed on
• Ex. Sickle cell allele is actually advantageous
  when malaria is present!!

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7 Give an example of a species that exhibits
sexual selection.

• Alces alces
• moose
• Pavo cristatus
• Peacock

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8 For each pattern of natural selection, give
an example of a species that exhibits the effects
of that selection.

• Any volunteers?? Come on up and I will find a
  picture.

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