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22 Cards in this Set
- Front
- Back
evolution |
change over time in allele frequencies of different alleles in a population |
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descent with modification |
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mutations |
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natural selection can be divided into 3 categories... |
1. direct 2. stabilizing 3. disruptive |
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direct selection |
occurs when individuals with one extreme of a heritable phenotypic trait are favored over other individuals |
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stabilizing selection |
individuals with intermediate phenotype are favored |
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disruptive selection |
individuals with phenotype at either extreme are favored |
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gene flow |
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genetic drift |
occurs when chance events affect which alleles are passed from one generation to the next |
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four effects of genetic drift on evolution in small populations |
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adaptive evolution |
a process of change in which traits that confer survival or reproductive advantages tend to increase in frequency over time...enhances fitness |
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clines |
patterns of change in a characteristic of an organism over a geographic region |
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constraints on adaptive evolution |
1. lack of genetic variation 2. evolutionary history 3. ecological trade-offs |
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lack of genetic variation |
if none of the individuals in a population has a beneficial allele of a particular gene that influences survival and reproduction, adaptive evolution cannot occur at that gene |
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evolutionary history |
natural selection brings about changes by modifying traits that are already present in an organism, not by creating advantageous traits from scratch |
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ecological trade-offs |
trade-offs occur in all organisms and they ensure that adaptation will never be perfect…instead, adaptations represent comporomises in the abilities of organisms to perform many different and sometimes conflicting functions |
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speciation |
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how do new species evolve? |
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allopatric speciation |
geographic barrier present |
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sympatric speciation |
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parapatric speciation |
occurs when populations are separated by an extreme change in habitat |
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adaptive radiation |
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