BIOL 2200 Lecture Notes - Lecture 5: Natural Selection, Sexual Selection, Genetic Drift

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Mutation little effect on its own, but key to other processes. Gene flow important unless populations are isolated. Genetic drift extremely important, particularly in small populations. Natural selection extremely important in most populations. Gene flow can increase or decrease genetic variation. Directional selection = selection acting on one phenotype, shifting it. Same bell curve, just in a different direction. Ex: severe drought dried up smaller seeds, meaning larger seeds were more available. Stabilizing selection = selection favors the average phenotype. Ex: snow goslings that hatch in the timeframe that all the others hatch is more likely to protect you than if you were born before or after the others. Disruptive selection = average phenotype is the least favorable phenotype. Bell curve turns into an m shape. Ex: when only hard seeds and soft seeds are available, only finches with either large beaks or small beaks will be more likely to survive.

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