Variation and mutation

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Example:

50 individuals = 100 alleles

25 R alleles = 25/100 = 25% R = 0.25 is the frequency of R

75 W alleles = 75/100 W = 75% W = 0.75 is the frequency of W

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Allele frequency

Note:

The sum of the frequencies for each allele in a population is always equal to 1.0!

Frequencies are percentages, and the total percentage must be 100

100% = 1.00

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Other important frequencies

Genotype frequency

The percentage of each genotype present in a population

Phenotype frequency

The percentage of each phenotype present in a population

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Evolution

Now we can define evolution as the change in genotype frequencies over time

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Genetic Variation

The very stuff of evolution!

Without genetic variation, there can be no evolution

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Pigeons

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Guppies

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Why is phenotypic variation not as important?

Phenotypic variation is the result of:

Genotypic variation

Environmental variation

Other effects

Such as maternal or paternal effects

Not completely heritable!

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Hardy-Weinberg Equilibrium

Five conditions under which evolution cannot occur

All five must be met:

If any one is violated, the population will evolve!

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HWE: Five conditions

No net change in allele frequencies due to mutation

Members of the population mate randomly

New alleles do not enter the population via immigrating individuals

The population is large

Natural selection does not occur

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HWE: 5 violations

So, five ways in which populations CAN evolve!

Mutation

Nonrandom mating

Migration (Gene flow)

Small population sizes (Genetic drift)

Natural selection

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Math of HWE

Because the total of all allele frequencies is equal to 1…

If the frequency of Allele 1 is p

And the frequency of Allele 2 is q

Then…

p + q = 1