BSC 196 Lecture Notes - Lecture 6: Genetic Drift, Balancing Selection, Mate Choice

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17 Feb 2017
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Three major evolutionary forces that cause change: Gene flow consists of the movement of alleles among population. Alleles can be transferred through the movement of fertile individuals or gametes (sperm/egg) Evolution by natural selection involves both chance and sorting . New genetic variations arise by chance (mutations) Beneficial alleles are sorted and favored by natural selection (non- random) Directional- favors individuals at one extreme end of the phenotypic range. Disruptive- favor individuals at both ends of the phenotypic range. Stabilizing- favors intermediate variants and acts against extreme phenotypes. Size, strength, coloration, weaponry, sexual signaling, ornamentation. Sexual selection favors traits that promote mating success. Good genes hypothesis: if a trait reveals genetic quality or health, females should select based on that trait. Leads to increase in frequency of both the trait and preference. Preferences for high-calling males in gray tree-frogs. Occurs when natural selection maintains stable frequencies of two or more phenotypes in a population.

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