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Evolution of Populations and Speciation

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Terms in this set (23)

  • What are the three major factors that alter allele frequencies and drive evolutionary change?
    Natural selection, genetic drift, and gene flow.
  • Define natural selection.
    Differential reproductive success causes certain alleles to be passed on more frequently, leading to adaptive evolution.
  • What is the founder effect?
    When a few individuals become isolated from a larger population, causing allele frequencies in the new population to differ from the original.
  • Describe the bottleneck effect.
    A sudden reduction in population size due to environmental change, leading to a gene pool that may not represent the original population.
  • How does genetic drift affect small populations?
    It causes random changes in allele frequencies, loss of genetic variation, and can fix harmful alleles by inbreeding.
  • What is gene flow?
    The movement of alleles among populations through migration or gamete transfer, which can increase or decrease fitness.
  • Define relative fitness.
    The contribution an individual makes to the gene pool of the next generation compared to others.
  • Name the three modes of natural selection.
    Directional, disruptive, and stabilizing selection.
  • What is directional selection?
    Selection that favors individuals at one extreme of a phenotypic range.
  • What is disruptive selection?
    Selection that favors individuals at both extremes of a phenotypic range.
  • What is stabilizing selection?
    Selection that favors intermediate phenotypes and acts against extremes.
  • How does natural selection cause adaptive evolution?
    By increasing the frequency of alleles that improve survival and reproduction in a changing environment.
  • What is sexual selection?
    Natural selection for mating success, often causing sexual dimorphism.
  • Explain heterozygote advantage.
    When heterozygous individuals have higher fitness than either homozygote, maintaining genetic variation.
  • What is frequency-dependent selection?
    Selection where the fitness of a phenotype decreases if it becomes too common, favoring rarer phenotypes.
  • What is the biological species concept?
    A species is a group of populations whose members can interbreed and produce viable, fertile offspring.
  • Define reproductive isolation.
    Biological barriers that prevent two species from producing viable, fertile offspring.
  • Name two types of reproductive isolation barriers.
    Prezygotic (before fertilization) and postzygotic (after fertilization) barriers.
  • What is allopatric speciation?
    Speciation that occurs when populations are geographically isolated, reducing gene flow.
  • What is sympatric speciation?
    Speciation occurring within overlapping populations due to factors like polyploidy or sexual selection.
  • How can polyploidy lead to speciation?
    By producing extra chromosome sets, creating new species especially in plants.
  • What is punctuated equilibrium?
    A model where species experience long periods of stasis interrupted by sudden evolutionary change.
  • What limits natural selection from producing perfect organisms?
    Selection acts only on existing variation, historical constraints, compromises in adaptations, and chance events.