Hardy-Weinberg Genetic Equilibrium

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Hardy-Weinberg Genetic Equilibrium
Flamingo population
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Remember to maintain equilibrium

1. No change due to mutations.
2. Individuals do not move in or out of the
   population.
3. The population is and remains large.
4. Random mating.
5. No selection

Tule Elk population at Pt Reyes
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Disruption of Genetic Equilibrium

• If any of the 5 factors occur, they can cause the
  gene frequency to change in a population.
• If the gene frequencies change evolution has
  occurred.

Tule Elk population at Pt. Reyes
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Mutations

• Mutations occur normally but at extremely low
  rates.
• Mutations do not cause gene frequencies to
  change.

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Migration

• Immigration (movement in) or emigration (movement
  out) can effect gene frequencies.
• Movement of individuals from one population to
  another results in gene flow.

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Genetic Drift

• Small populations are subject to genetic drift.
• Random events lead to changes in gene frequencies.

Each line represents a different population. Each
starts with the same number of allele A. over
time the number of individuals with that allele
changes. If a population is small enough over
several generation the allele will either be 0 or
100 present.
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Nonrandom Mating

• Random mating throughout a population does not
  occur.
• Geographical regions.
• Sexual selection
• Ex birds of paradise
• Assortive mating
• Ex Fruit flies.

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Directional Selection

• Wild pigs impose selection upon the cactus
  population.
• Cactus that have fewer needles do not survive to
  reproduce.
• Cactus with more needles survive to reproduce.

Cactus and wild pigs
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Directional Selection results

• Result of directional selection is a shift in the
  population towards more spines.
• One extreme is selected for and one against.
• Ex cliff swallows after a cold snap.

Ive posted a short article on how cliff swallow
wing length has shorted due to new selective
pressures. Read it and refer to it in your
summary.
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Stabilizing Selection

• Both extremes are selected against.
• The average is selected for.
• Population becomes more similar due to average
  being selected for.
• Ex human birth weight

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Disruptive Selection

• Extremes are selected for.
• Results in two distinctly different populations.
• Disruptive selection can lead to two species.
• Average is selected against.
• Ex finches in west Africa, eat different sized
  seeds.

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Calculating allele frequencies

• Use the Hardy-Weinberg equation
• p²  2pq  q²  1
• q is the recessive trait and q² is homozygous
  recessive
• p is the dominate trait and p² is homozygous
  dominant.
• pq is heterozygous
• added together you have 100 of the individuals
  in a population

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Disruption of Genetic Equilibrium - Summary of
Selection
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Summary Review

• Describe the 3 types of selection.
• What is genetic drift, what causes it, an what
  results from it?
• What can cause new genes to enter a population?
• What do these two pictures illustrate?