HardyWeinberg Conditions

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• Hardy-Weinberg Conditions
• Random Mating
• No Net Mutations
• No Net Migration
• Large Population Size
• All Individuals Equally Fit
  (No Natural Selection)

When one or more conditions are violated, then
the population is evolving (i.e., allele
frequencies are changing). Natural Selection is
only ONE cause of evolution.
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Non-Random Mating
FF Ff
ff
Lots of FF Few Ff ff
All ff
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Net Mutations
10 of F to f 10 of f to F
30 of F to f 10 of f to F
F
f
F
F
f
F
f
f
f
f
F
F
F
F
F
f
f
f
f
F
f
f
F
f
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Net Migrations
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Small Population Size
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Small Population Size
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• Requirements for Natural Selection
• Phenotypic variation among individuals
• Differential fitness among phenotypes
• Genetic basis for phenotypes

Natural Selection can only work on
phenotypes Selection can be Stabilizing (mean
favored) Disruptive (two extremes
favored) Directional (one extreme favored)
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Stabilizing
Disruptive
Directional
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Terms to get straight Natural Selection
Differential survival and reproductive success of
individuals based on genetically based
differential phenotypes. (3 requirements) Evoluti
on A change in allele frequencies over time
within a population. (5 causes) Stabilizing
vs. Disruptive vs. Directional Selection
Stabilizing selection results in the same mean
but lower variability. Disruptive selection
results in a bimodal distribution.
Directional selection results in the same
variability, but a different mean.
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