BSC 196 Lecture 7: Bio- Lecture 7

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8 Feb 2017
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Wednesday, February 8, 2017
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Modes of selection
Gene flow
- Gene flow consists of the movement of alleles among populations
- Alleles can be transferred through the movement of fertile individuals or gametes (for
example, pollen)
- Gene flow tends to reduce variation among populations over time
Overview of Natural Selection
- Evolution by natural selection involves both chance and sorting
New genetic variations arise by chance (mutation)
Beneficial alleles are sorted and favored by natural selection (non-random)
- Only natural selection consistently increases the frequencies of alleles that provide
reproductive advantage
Modes of Selection
- There are three modes of selection
Directional selection favors individuals at one extreme end of the phenotypic range
Disruptive selection favors individuals at both extremes of the phenotypic range
Stabilizing selection favors intermediate variants and acts against extreme
phenotypes
Sexual Selection
- sexual dimorphism
size, strength, coloration, weaponry, sexual signaling, ornamentation
- sexual selection favors traits that promote Mating success
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