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Virtual Explorations
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Visit our textbook-specific Online Learning Center Web site at www.mhhe.com/relethford8e to access the exercises that follow.

  1. The Hardy-Weinberg Equilibrium Model

    2. http://anthro.palomar.edu/synthetic/synth_2.htm.
    "The Hardy-Weinberg Equilibrium Model" part of the larger "Synthetic Theory of Evolution" (Dr. Dennis O'Neil, Web site Behavioral Sciences Department, Palomar College) provides an excellent introduction and foundation in explaining both the theory of evolution in general and the Hardy-Weinberg model specifically.

    Read through the text. Click on the "Sample Problem" link http://anthro.palomar.edu/synthetic/sample.htm, which covers "Albinism."

    • Were you able to follow the formula through the various steps?
    • Has this helped clarify the theory for you?
    • Why are there more carriers of this trait than albinos?
    • Return to the earlier link and reread the description of Hardy-Weinberg if not.

  2. Natural Selection: Modes of Selection

    3. http://www.evotutor.org/Selection/Sl5A.html.
    Visit the EvoTutor simulation Web site, "Natural Selection: Modes of Selection." If you do not see a diagram on the right-hand side, click the apple in the upper right corner to open an applet window.

    Read through the three general modes of selection in a population. Check "Frequency" at the top of the diagram. Check "Directional selection" at the bottom of the diagram. Now run the simulator for mean color in a population.

    • What happens to the color frequencies in the population?
    • Now run the simulator for both "Stabilizing selection" and "Disruptive selection."
    • How do these results differ from each other? How are they different from the results of "Directional selection"?
    • Which selection mode plays the greatest role in speciation?

    Check "Histogram" at the top of the diagram, and run each simulation again to see a different way of visualizing natural selection operating on a population.

  3. The Micro Evolution Program: Allele Frequency Exercise

    4. This exercise requires the Micro Evolution Program by John Relethford. You will find the link on the home page for your book (http://highered.mcgraw-hill.com/sites/0072963816/student_view0/micro_evolution_program.html) under Course-wide Content. Download the program (1.4 megabytes).

    Plot the natural selection curve for a population using the Natural Selection function button. Assume your initial allele frequency is 0.5 (50:50 ratio of recessive to dominant alleles). Plot for q, which is the frequency of a, the recessive allele. Assume that natural selection is operating against the recessive homozygote (aa). This means that the fitness values are AA = 100, Aa = 100, and aa = 0.

    • What pattern does the recessive allele frequency (q) show after 100 generations? Why? What disease is an example of this selective force?
    • Now assume that natural selection is operating against the dominant allele (A). Also assume that partial selection is at work, so that the fitness values are AA = 50, Aa = 50, and aa = 100.
    • What pattern does the recessive allele frequency (q) show after 100 generations? Why? Now plot for the dominant allele frequency (p). What pattern does the dominant allele frequency show after 100 generations? Why? What disease is an example of this selective force?

  4. The Micro Evolution Program: Genetic Drift-Multiple Groups Exercise

    5. This exploration uses the Micro Evolution Program by John Relethford (see above). Experiment with the Genetic Drift-Multiple Groups plotting function.

    Plot the allele frequency over time (p), using a small population size, such as 2 or 5 individuals. Try it several times, using a different number of populations (2–6). What happens to the allele frequency?

    Now plot the allele frequency with a large population size, such as 100 or 200. Try it several times, using a different number of populations.

    • What happens to the allele frequency?
    • Is genetic drift operating equally on small and large populations? Is the allele ever lost completely?
    • Come up with a scenario in which an allele might be lost from an actual population. Under what circumstances could this take place?





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