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Ickle-cell anemia first appeared in Asia, the Middle East, and Africa. The causative allele entered the U.S. population when people were forcibly brought over from Africa prior to the Civil War. In microevolutionary terms, this is a case of _____ .
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Gene flow
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Directional selection occurs when
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The organisms on one extreme of the population have a better chance to survive than do those on the other extreme
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Stabilizing selection occurs when
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The extremes of the population have a lesser chance to survive
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The introduction of a small population onto an island that results in a limited gene pool for a population best describes
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The founder effect
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The sharp reduction of the gene pool and the numbers of a population through a severe epidemic is an example of
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The bottleneck effect
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Natural selection may occur when there are _____ .
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A. differences in the adaptiveness of forms of traits to prevailing environmental conditions
b. differences in survival and reproduction among individuals that differ in one or more traits c. both a and b |
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Directional selection ____.
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Sizeshifts allele frequencies in a steady, consistent direction
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Disruptive selection _____.
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Doesn't favor intermediate forms of a trait
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In the biological species concept of Ernst Mayer, what aspect of a population is critical to determining a species?
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Interbreeding capabilities
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Members of the same species would be expected to
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Share the same gene pool
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Two individuals are members of the same species if they
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Can mate and produce fertile offspring
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Sexually reproducing individuals of a species _____ .
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A. can interbreed under natural conditions
b. can produce fertile offspring c. have a shared genetic history d. all of the above |
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The primary reason for hybrid sterility is
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The difficulty in the pairing of homologous chromosomes
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Isolating mechanisms that take effect before or during fertilization are termed
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Prezygotic
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Hybrid inviability is an example of what kind of isolation?
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Postzygotic
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