Chapter 18.txt

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carlyandgenie
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57863
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Chapter 18.txt
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2011-01-03 01:30:54
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AP Biology
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Chapter 18
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  1. adaptation
    [L. adaptare, to fit] Any long-term, heritable aspect of form, function, or behavior that improves an individual�s chances of surviving and reproducing; outcome of natural selection and other microevolutionary processes.
  2. allele frequencies
    Abundance of one allele relative to others at a gene locus among individuals of a population.
  3. alleles
    One of two or more molecular forms of a gene at a given locus; alleles arise by mutation and encode slightly different versions of the same trait.
  4. balanced polymorphism
    An outcome of natural selection against homozygotes, so that two or more alleles for a trait are being maintained in the population.
  5. bottleneck
    Severe reduction in the size of a population, brought about by intense selection pressure or a natural calamity.
  6. dimorphism
    Persistence of two forms of the same trait in a population.
  7. directional selection
    Mode of natural selection by which forms at one end of a range of phenotypic variation are favored.
  8. disruptive selection
    Mode of natural selection that favors different forms of a trait at both ends of a range of variation; intermediate forms are selected against.
  9. emigration
    Permanent move of one or more individuals out of a population.
  10. evolution
    [L. evolutio, an unrolling] Genetic change in a line of descent by microevolutionary events (gene mutation, natural selection, genetic drift, and gene flow); basis of large-scale patterns, rates, and trends in the history of life.
  11. fixation
    Of a population, the loss of all alleles but one at a gene locus; all individuals have become homozygous for the allele.
  12. founder effect
    A form of bottlenecking. By chance, a few individuals that establish a new population differ in allele frequencies relative to the original population.
  13. gene flow
    Microevolutionary process; alleles enter and leave a population by immigration and emigration. Counters mutation, natural selection, and genetic drift, hence reproductive isolation.
  14. gene mutation
    Small-scale change in the nucleotide sequence of a gene; can result in an altered protein product.
  15. genetic drift
    Change in allele frequencies over generations due to chance alone. Most pronounced effects in small populations.
  16. genetic equilibrium
    In theory, a state in which a population is not evolving with respect to a specified gene locus. Compare Hardy�Weinberg rule.
  17. Hardy�Weinberg equilibrium equation
    Theoretical baseline for tracking changes in allele frequencies over the generations. Frequencies do not change as long as there is no mutation, the population is infinitely large and isolated from other populations, and all individuals are reproducing equally and randomly.
  18. immigration
    One or more individuals move and take up residence in another population of its species.
  19. inbreeding
    Nonrandom mating among very close relatives that share many identical alleles; may fix harmful alleles.
  20. lethal mutation
    Mutation having drastic effects on phenotype; usually causes death.
  21. microevolution
    Of a population, a smallscale change in allele frequencies resulting from mutation, genetic drift, gene flow, natural selection, or a combination of them.
  22. neutral mutation
    A mutation with no effect on phenotype; natural selection thus cannot change its frequency in a population.
  23. polymorphism
    [Gk. polus, many,+morphe, form] Persistence of two or more qualitatively different forms of a trait, or morphs, in a population.
  24. population
    All individuals of the same species living in a specified area.
  25. probability
    The odds that each outcome of an event will occur is proportional to the total number of ways in which that outcome can be reached.
  26. sexual dimorphism
    A notable difference between female and male phenotypes of a population.
  27. sexual selection
    A category of natural selection; an outcome of differences in success at attracting mates and reproducing among individuals of a population.
  28. stabilizing selection
    Mode of natural selection; intermediate phenotypes are favored over extremes at both ends of the range of variation.

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