Many fish species have a gas-filled swim bladder that can adjust in size to make the density of the fish’s body equal to that of the surrounding water.

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#Unit 11. Evolution and Behavior

The allelic frequency at equilibrium (qˆ) depends on the relative fitnesses (usually expressed as selection coefficients) of the two homozygotes:

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#Unit 11. Evolution and Behavior

Hitchhiking

An important consequence of linkage disequilibrium is hitchhiking. This happens when an allele at  one locus spreads by natural selection acting on a second locus that is in linkage disequilibrium with  the first.

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#Unit 11. Evolution and Behavior

Type of natural selection

1. Stabilized natural selection

2. Directional Natural selection

3. Disruptive Natural selection

4. Balance natural selection

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#Unit 11. Evolution and Behavior

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#Unit 11. Evolution and Behavior

Stabilized natural selection

Favor intermediate phenotype but eliminate lower and higher-grade phenotype

It introduced homogeneity in the population

Exp - clutch size of birds that lay too many or too few eggs per nest have lower fitness values than do those that lay an intermediate number of eggs

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#Unit 11. Evolution and Behavior