The exercise presented here is a hands-on demonstration of the phenomenon of genetic drift in populations. In particular, it reinforces the random nature of drift and demonstrates the effect that population size can have on the mean frequency of an allele over just a few generations. The students will take on the roles of organisms (with genotypes) and they will choose mates and generate offspring themselves (on note cards). The frequency of each genotype in the population will be recorded over time. From this the allele frequencies for the population can be calculated. The students will see that by simply choosing mates using a random-mating system, they will generate allele frequency dynamics.