that went to fixation after six generations and another that lasted
16 generations (Figure 2). This degree of variation presented a challenge to keep all students engaged. After field testing the project,
I recommend having additional data sheets (Figure 1) on hand
and having groups that finish early engage in additional simulations
to add to the data set.
After completion of the project, there are a number of ways to
proceed. Before a class-wide discussion of the results from all
groups, students could be asked to graph their group’s results and
answer questions about their findings. For example, how would
increasing the sample size impact the magnitude of generation-to-generation changes and/or the time to fixation of one allele? How
would a more diverse gene pool (i.e., more than two alleles) impact
the results? (Etc.)
In conclusion, this project – a relatively simple undertaking
with modest supplies – helps illustrate genetic drift due to sampling
error in a concrete, hands-on way. Completing this project (alone
or in combination with extensions such as those described above)
before a discussion of computer simulations of populations of vari-
ous sizes would allow students to better understand both the
mechanism of drift and the influence of population size on its
impacts on populations.
I thank K. T. Elliott for helping test this project and providing feedback on it. M. A. Wund and anonymous reviewers provided feedback on the manuscript.
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Table 1. The pair of individuals selected for a
mating corresponding to each possible roll of the die.
Roll Result Mating Pair (Individuals)
1 1 and 2
2 1 and 3
3 1 and 4
4 2 and 3
5 2 and 4
6 3 and 4
Figure 2. The frequency of allele A1 over generational time
from four simulations.