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GEEslidesSet6 1April2010

GEEslidesSet6 1April2010 - NATURAL SELECTION AND ADAPTATION...

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NATURAL SELECTION AND ADAPTATION http:// hometown.aol.com/cre82 / From Logan’s Animal Adaptation Page:
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EXPLANATIONS OF ADAPTATIONS Most adaptations are complex. They usually look like they were designed for some function. WHAT DOES EVOLUTIONARY THEORY NEED TO EXPLAIN? The origin of complex adaptations. Features that seem not to benefit individuals, such as genetic recombination, sex ratios, and senescence. Apparent failures of adaptation -- a bee must kill itself to deliver a sting, male insects that are eaten by their mates.
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EXPERIMENTAL STUDIES OF NATURAL SELECTION Microorganisms Mutants of the gene for β-galactosidase (enzyme that break down sugar) were grown on lactose in competition with wild type Escherichia coli .
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EXPERIMENTAL STUDIES OF NATURAL SELECTION Hitchhiking A ° °   A neutral allele can increase in frequency by being in linkage disequilibrium with a selectively advantageous allele. This process is particularly important in organisms or chromosomal regions with low rates of recombination. SELECTION FOR BLUE ALLELE Taken to the extreme, the result is a SELECTIVE SWEEP .
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TWO IMPORTANT POINTS SO FAR 1. Adaptation results from a difference in the rates of reproduction of different genotypes caused by a difference in some property of those genotypes . 1. Natural selection results from adaptation 2. Natural selection may increase the frequency of a characteristic, not because the characteristic enhances survival and reproduction, but because it is correlated with another characteristic that does so.
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EXPERIMENTAL STUDIES OF SELECTION Drosophila pseudoobscura Dobzhansky studied the frequencies of chromosomal inversion polymorphisms in nature and the lab. STABLE EQUILIBRIUM
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FEMALE PREFERENCE FOR TAIL LENGTH IN WIDOWBIRDS Nesting success before experimental manipulation Nesting success after experimental manipulation
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EXPERIMENTAL STUDIES OF SELECTION Male reproductive success
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MALE-MALE COMPETITION Male Red Deer with the greatest success in combat are able to retain females for longer periods.
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SEXUAL SELECTION Selection that arises as a result of competition for access to mates. Intrasexual selection typically refers to male-male competition. Intersexual selection typically refers to female choice of males. Sexual selection may oppose natural selection in the sense that traits that enhance mating success may decrease survival or other aspects of fitness.
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EXPERIMENTAL STUDIES OF NATURAL SELECTION Evolution of population size in Tribolium An example of group selection.
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THE PROBLEMS WITH GROUP SELECTION Good group selection Losing traits b/c of migration of cheaters in. Have traits beneficial to individual not group
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THE PROBLEMS WITH GROUP SELECTION 1. If individual selection and group selection both favor the same trait, then group selection will never occur, because individual selection will prevail .
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