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Chapter 13 T6-T9 - Notes from Friday January 25 Under...

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Notes from Friday, January 25 Under Topic #6 – Natural selection and population B. Effects of selection on populations 1. Stabilizing selection a. reduces variation b. does not change mean 2. Directional selection a. changes mean in one direction 3. Disruptive (diversifying) selection a. favors extremes over intermediate forms C. Types of selection 1. kin selection – relative contribution of a genotype is increased by ‘cooperation’ among close relatives a. scrub jays – ‘nest helpers’; first year birds help parents feed next generation b. prairie dogs – alarm calls c. eusocial species – ‘true social’; ants, bees, termites, naked mole rat i. include many sterile individuals ii. increase genetic relation (all same mom) iii. increase benefit to ‘cooperate’ 2. sexual selection – selection that favors traits which improve an individual’s chances of mating (sexiness) a. benefit – increased mating b. costs – increases predation risk, bulky appendages (elk antlers, peacock feathers)
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