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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?
    Answer
  4. What are the five prezygotic isolating mechanisms?
    Answer
  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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