General Biology Independent Laboratory Experiences for the College Science Major
Second Semester
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The Hardy-Weinberg Principle

Exercise 1: The Hardy-Weinberg Equilibrium Model

Hitchhiker’s
Thumb Thumbs with end joints that can be bent back at 45 are 100% recessive (ss).

Thumbs that cannot bend back significantly are dominant (either SS or Ss). SS, Ss ss Students’ Results: 78 56

Results:

1. Use Example 1 as a guide and the students’ data above to determine the allelic frequencies for the gene using the equations proposed by Hardy-Weinberg to support the equilibrium theorem.

2. Show that the allelic frequencies will not change over time.

3. Suggest conditions that could change these frequencies. What would the effects of the conditions be?

Exercise 2: Evolution and Genetic Drift

Results:

Table 1: Student’s Results for an Ecological Study to Determine Genetic Drift Due to Selective Foraging Pressure by a Kestrel generation # of brown grasshoppers B? # of green grasshoppers bb q2 q p P2 2pq
Y0
Y1
Y2
Y3
Y4
Y5

For purposes of calculation: Let p = the frequency of the dominant allele, B. Let q = the frequency of the recessive allele, b. ? can denote either B or b. Why?

Table 2: Class Results for an Ecological Study to Determine Genetic Drift Due to Selective Foraging Pressure by a Kestrel generation Avg # of brown grasshoppers Genotype B?
N* = ________
(at least 3 sets) Avg # of green grasshoppers Genotype bb
N* = ________
(at least 3 sets) q2 q p P2 2pq
Y0
Y1
Y2
Y3
Y4
Y5
For purposes of the calculation: Let p = the frequency of the dominant allele, B. Let q = the frequency of the recessive allele, b. ? can denote either B or b. Why?
* N = Number of data sets from other students that are averaged for this number. Fill in.

Figure 1: Comparison of Grasshopper Allele Frequency with Time as a Function of Grazing Pressure
P = frequency of B, allele for Brown color q = frequency of b, allele for Green color Student data (Table 1.2.1) recorded in_______________. Class data (Table 1.2.2, if available) recorded in ______________.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Y0 Y1 Y2 Y3 Y4 Y5

Conclusions:

1. Briefly describe your results from the graph and Table 1 in writing. What patterns do you observe? Which allelic frequency was highest at the beginning (Y0)? Which allelic frequency was highest at the beginning of Year 5, Y5?

2. If you had the opportunity to obtain classmates’ data, how do your results compare to the class’ results in Table 2 and in the graph, Figure 1? Why is it important to obtain the class’ results as a comparison to your own?

3. What conditions in the study would have had to exist in order for both allelic frequencies to remain at 0.5?

4. Which genotype was environmentally unfavorable for grasshopper color in this study? Why?

5. If the study were continued, would one allele eventually disappear altogether? Why or why not? Why might this be important?

6. What part of this exercise could potentially NOT be representative of a naturally breeding population?

7. What parts of the Hardy-Weinberg Theorem were violated in the Hungry Kestrel exercise?

Discussion:

1. What process is occurring when allelic frequencies for a specific gene change over a long period of time? Is there an alternate explanation? If so, what is it?

2. How can the kestrel study be compared to what happens in a population of bacteria exposed to an antibiotic? How is the study similar? Different?

3. Prior to the beginning of England’s industrial revolution in 1740, the Peppered Moth, Biston betularia, spent its days on the trunks of trees containing light-colored lichen on dark tree trunks. The typical color of the moth was light with black spots due to the high frequency of recessive alleles for light color although a few dark-bodied individuals possessing the dominant gene for dark color also survived in the moth population. After the industrial revolution was well underway, ecologists noted that the moth body color had shifted to the dark color almost exclusively. They also noted that the smoke and air pollution from industrial processes had adversely affected the presence of lichen on tree trunks so that very little remained.
Pose a scenario that would explain why the moth population exhibited this color change. What would have caused this and the disappearance of lichens?

4. Do organisms consciously choose to evolve? Explain your answer.

5. Give hypothetical or actual examples to demonstrate how each of the five conditions (migration, isolation, no selection, no random mating, small population size, mutations) of the Hardy-Weinberg equilibrium can be violated.

6. As a research scientist what steps could you take to prevent a bacterial culture from evolving so that you could conduct a controlled experiment reaction to a specific drug under development?

Laboratory Summary:

What have you learned from doing this laboratory?

References Consulted: (must be in correct citation syntax for full credit)