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Chapter 17.2: Evolution as Genetic Change in Populations.

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Presentation on theme: "Chapter 17.2: Evolution as Genetic Change in Populations."— Presentation transcript:

1 Chapter 17.2: Evolution as Genetic Change in Populations

2 Natural Selection on Single-Gene Traits -Natural selection selects for traits -Genes create traits -There can be a wide variation in traits and genes -Some traits are a better fit for the environment than others, so the genes that create them are also a better fit

3 Directional Selection -Polygenic traits, like height or size, have many variations -One extreme phenotype in the range of variation has higher fitness than others -This phenotype is favored and selected for

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5 Stabilizing Selection -Individuals with intermediate (medium, average) phenotypes have higher fitness than others -This phenotype is favored and selected for

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7 Disruptive Selection -Individuals with both types of extreme phenotypes have higher fitness than others -These phenotypes are selected for, and the intermediate phenotype is selected against

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9 Genetic Drift -Is a random change in allele frequency -An allele can become more or less common in a population by chance -Occurs more frequently in small populations -Can be caused by human actions, disease, or natural disasters

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11 Bottleneck Effect -Is a change in allele frequency following a catastrophic reduction in the size of a population -Can sharply reduce a population’s genetic diversity

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13 Founder Effect -Is when a small group from one population leaves and founds a new population elsewhere -The founding group that left may have different allele frequencies than the original population

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