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10-Natural selection review

10-Natural selection review - Natural Selection Revisited s...

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Unformatted text preview: Natural Selection Revisited s Evolution - Changes in allele frequencies in a population over time. s Natural selection - one agent of evolution x The only one that leads to a fit between characteristics of organisms and their environment. s Other agents of evolution include: x Mutation x Migration x Genetic drift Types of Natural Selection s Directional selection x One end of the distribution is favored s Stabilizing selection x Middle of the distribution is favored s Diversifying selection x Both ends of the distribution are favored, relative to middle Types of Natural Selection Disruptive See Section 25.2 Directional Selection s Peppered Moths x Industrial melanism (there and back again thanks to scrubbers!) Directional Selection s Peppered Moths today (See section 24.3) Directional Selection s Horse size evolution Directional Selection s Darwin's finches xWhen rainfall conditions changed- beak size shifted. See 24.13 Stabilizing Selection s Human birth weight Stabilizing Selection s Human birth weight Stabilizing Selection s Ex: Siberian Husky s Average size (35-60 lbs.) is optimal for these dogs bred for working in the snow. x Too heavy 3 Sink in snow x Too light 3 Not strong enough Disruptive Selection s Black-bellied seed crackers x Middle range of beak size don't survive x Poor for handling small seeds x Can't crack large seeds See Fig. 25.5 Disruptive Selection s Coho Salmon x Two size classes of males 3 "Jack" and "Hooknose" x Large males more attractive, better fighters Disruptive Selection s Coho Salmon x Small males can be more "sneaky" Density Dependent Selection s Scale eating cichlidsx Feeds off the scales of living fish (lepidophagy!) x Some better at scraping on the left side, others better at scraping on the right side. Summary s Natural selection is a very powerful agent of evolutionary change x Other agents include mutation, migration, drift s Natural selection can be: x directional x stabilizing x disruptive x density dependent ...
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