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Lect. 03 - evol prt 2 web - Populations Are the Units of...

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Populations Are the Units of Evolution Populations Are the Units of Evolution Population : group of individuals of same species living in the same place at the same time Species : interbreeding individuals Natural Selection operates on Populations Genetic Variation = raw material for Natural Selection So, we keep track of Variation in Populations… Human populations tend to concentrate locally, like most other organisms
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Natural Selection can favor, disfavor, or conserve alleles within populations… Fitness = individual contribution of offspring, or genes, to future generations. Differential reproductive success Different phenotypes = Variation Raw material = Variation Green = Higher Fitness
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Stabilizing Selection Stabilizing selection favors average phenotypes. Impeeds change…
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Directional Selection Directional selection favors extreme phenotype over others .
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Disruptive Selection Favors two or more extreme phenotypes over the average (= higher variation).
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But wait, variation can also be due to environment Phenotypic Plasticity = variation due to environmental influence only (organisms look different despite same genes) Overall variation (Vp) = genetic variation (Vg) + environmental variation (Ve) i.e., some variation is NOT inheritable…
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Evolution by Natural Selection adaptations – only result from inheritance, so ecologists often measure genetic contributions to a trait heritability = measure of inheritance.
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