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18.1 Evolution in a Genetic Context
  • The Hardy-Weinberg law defines evolution in terms of allele frequency changes in a population over time.
  • Mutations, gene flow, nonrandom mating, genetic drift, and natural selection can cause allele frequency changes in a population.
  • The raw material for evolutionary change is mutations. Recombination of genes is another source in sexually reproducing organisms.
  1. Evolution that occurs within a population is called _______________.
    Answer
  2. What is the gene pool of a population?
    Answer
  3. What are the frequencies of the B and b alleles in a population made up of 35 BB, 40 Bb, and 25 bb individuals?
    Answer
  4. What are the equations p + q = 1 and p2 + 2pq + q2 = 1 used for?
    Answer
  5. What does each value in the expressions p + q and p2 + 2pq + q2 stand for?
    Answer
  6. What is Hardy-Weinberg equilibrium and what does it mean if a population is not in Hardy-Weinberg equilibrium?
    Answer
  7. What are the 5 conditions which must be met by a population in order for Hardy-Weinberg equilibrium to apply?
    Answer
  8. The movement of alleles from one population to another is called _______________, while the loss of alleles from a population due to random chance is called ________________.
    Answer
Essential Study Partner Summaries of major points:
  1. What causes variations?
  2. Microevolution
  3. Genetic mutations
  4. Gene flow
  5. Nonrandom mating
  6. Genetic drift
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18.2 Natural Selection
  • Natural selection causes changes in allele frequencies in a population due to the differential ability of certain phenotypes to reproduce.
  • Natural selection results in adaptation to the environment. The three types of natural selection are: directional selection, stabilizing selection, and disruptive selection.
  1. What happens during directional selection?
    Answer
  2. When intermediate phenotypes are selected against, the selection pressure is called ______________; but when the intermediate phenotype is the one favored, the selection pressure is called ______________.
    Answer
  3. How does heterozygosity prevent the loss of recessive alleles, even when they are deleterious?
    Answer
Essential Study Partner Summaries of major points:
  1. Natural selection is the process that results in adaptation of a population to the environment
  2. Types of selection
  3. Maintenance of variations
  4. Diploidy and the heterozygote
  5. Sicle-cell disease
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18.3 Speciation
  • New species come about when populations are reproductively isolated from other, similar populations.
  • Adaptive radiation is the rapid development of several species from a single species; each species is adapted in a unique way.
  1. What are the two major ways in which speciation can occur?
    Answer
  2. What is the biological definition of a species?
    Answer
  3. What are reproductive isolating mechanisms and what is their importance in maintaining species?
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  4. What are the five prezygotic isolating mechanisms?
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  5. Speciation occurring because of geographic isolation of populations is called ____________, while speciation occurring without physical isolation of populations is called ____________.
    Answer
  6. The rapid development and spread of many species from one to take advantage of open habitats is called what?
    Answer
Essential Study Partner Summaries of major points:
  1. Speciation is...
  2. A biological species is...
  3. Reproductive isolating mechanisms
  4. Modes of speciation
  5. Adaptive radiation







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