Population geneticsBio341

• Mutation - the ultimate source of all genetic variation

• Recombination - shuffles existing alleles

• Selection - different alleles and genotypes have different fitness. Frequencies change with time

• Migration - introduces alleles and genotypes into populations

• Drift - results in the loss of alleles from populations

Mutation and the fluctuation test

A population is:

• a group of individuals of the same species from which the next generation is drawn. (Often included is that members of the same population occupy the same locality and ecological niche.)

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Effect of strong selection

See: Kent Holsinger’s web site, Univ. Connecticut

See: Kent Holsinger’s web site, Univ. Connecticut

Consider a population that is:

• Haploid• Asexual (no recombination)• Not subject to any kind of selection

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Random numbers:1 3 1 4 3

Individuals

Generations

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Random numbers:3 4 3 5 1

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Random numbers:5 3 5 4 4

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Random numbers:5 1 5 1 3

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Random numbers:2 3 1 3 2

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Not all individuals leave behind descendants.

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Present individuals have a common ancestor.

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Present individuals have a common ancestor.

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Present individuals have a common ancestor.

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Present individuals have a common ancestor.

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Present individuals have a common ancestor.

For any pair of individuals, what is the chance of a common ancestor in the generation immediately preceding?

Answer: 1/N

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For any pair of individuals, what is the average time back to the most recent common ancestor?

Answer: N generations

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For any pair of individuals, what is the average number of mutational events separating them?

Answer: 2Nwhere is theRATE of mutation per gene (or per nucleotide) per generation.

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The effects of various forces on gene frequency

(A)

0.0 100.0

Mutationa to A

MutationA to a

drift

migration

Balancingselection

Directionalselection

Selectionagainst

heterozygotes