BIOL 103 Lecture Notes - Tribulus Terrestris, Daphne Major, Stabilizing Selection
8 Mar 2013
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Document Summary
Three general modes of selection on continuous (polygenic) traits: stabilizing. Favours the mean or typical individual: disruptive. Favours two or more phenotypic extremes at expense of individuals near the mean: directional. Stabilizing selection: birth weights of 13,730 babies in british hospitals . Stabilizing selection reduces the amount of variation in a trait. Disruptive selection: seedcracker finch populations in cameroon diverge if only large and small seeds available. Disruptive selection increases the amount of variation in a trait. Directional selection: observations that different size darwin"s finches eat different sized seeds on islands like daphne major. Natural selection during a drought average size of bird increased dramatically. Directional selection on different aspects of phenotype may constrain evolution of a trait like body size. Darwin: most selection in natural selection, but there is sexual selection, special category of traits that go against natural selection traits for sexual selection out weigh natural selection it is harder to study sexual selection in plants.
