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• Evolution is best defined as "descent with modification."
• Darwin's primary insight was to propose that evolutionary change resulted from the operation of natural selection.
• Selection is a powerful force leading to changes in populations but other processes may contribute. In any case, genetic variation is necessary for changes to occur.
• Invertebrates and outcrossing plants are often heterozygous at about 8 to 15% of their loci; the corresponding value for vertebrates is about 5 to 8%.
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1. What is the difference between natural selection and evolution?
2. What is adaptation? How does it fit into Darwin's concept of evolution?
3. What is genetic polymorphism? What has polymorphism to do with evolution?
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• Studies of how allele frequencies shift within populations allow investigators to study evolution in action.
• Meiosis does not alter allele frequencies within populations. The Hardy-Weinberg principle states that unless selection or some other force acts on the genes, the frequencies of their alleles remain unchanged from one generation to the next.
• A variety of processes can lead to evolutionary change within a population, including mutation, gene flow, nonrandom mating, genetic drift, and selection.
• For evolution to occur by natural selection, three conditions must be met: 1. variation must exist in the population; 2. variation must be related to the number of offspring left in the next generation; 3.the variation must have a genetic basis.
• Natural selection can usually overpower the effects of genetic drift, except in very small populations.
• Natural selection can overwhelm the effects of gene
flow in some cases, but not in others.
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4. Given that allele A is present in a large random-mating population at a frequency of 54 per 100 individuals, what is the proportion of individuals in that population expected to be heterozygous for the allele? homozygous dominant? homozygous recessive?
5. Why does the founder effect have such a profound influence on a population's genetic makeup? How does the bottleneck effect differ from the founder effect?
6. What effect does inbreeding have on allele frequency? Why is marriage between close relatives discouraged?
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• Disruptive selection acts to eliminate rather than to favor the intermediate type; directional selection acts to eliminate one extreme from an array of phenotypes; and stabilizing selection acts to eliminate both extremes.
• Natural selection is not all powerful; genetic variation
is required for natural selection to produce evolutionary change.
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7. Define selection. How does it alter allele frequencies? What are the three types of selection? Give an example of each.
8. Why are there limitations to the success of selection?
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