Evolution Lab 1: Do Beads Experience Genetic Drift and/or Natural Selection? By Team “Beads of Boom”

In this laboratory experiment, we examined the hypothesis that bead allele frequency changes over time, whether due to natural selection, or due to chance. The latter phenomenon is known as genetic drift. Our null hypothesis was that bead allele frequency does not change over time. Our prediction was that since none of the beads had an advantage to make them more likely to be picked, the allele frequency would change due to genetic drift rather than natural selection.

To test whether our bead frequencies changed over the course of ten generations, we compared the first-generation distribution (the “expected” population) with the tenth-generation distribution (the “observed” population) using Chi-square analysis. For the size of our population, the critical value for chi-square was 7.82. Population A’s chi-square value was 5.2, and Population B’s chi-square value was 0.58. Although these low values would seem to support the null hypothesis, we also compared our results with the populations of the rest of the lab class (see Table 1 below). Out of the four additional populations, all had a higher chi-square value than the critical value.

Based on all populations, we concluded that the null hypothesis should be rejected. Detailed examination of the data shown in Figure 1 shows that no particular color of bead increased more than another, which would be expected if the changing frequencies were due to natural selection. Although our two populations of allele bead frequency did not change significantly, an unchanging population fits in a model of random change.

Figure 1: Allele distribution (represented by colored beads) in populations A and B. Beads were chosen at random then doubled for 10 generations. Allele frequency showed little to no change between generation 1 and 10.

Table 1. Comparison of Chi-Square Analysis of Bead Populations between generations 1 and 10 with the null hypothesis being there was no significant change in allele frequency.

Team	Chi-Square value	Critical Value	Support/Reject Null Hypothesis
Nhy & Anh	14.6	7.82	Reject Null
Brian & Prach	13.4	7.82	Reject Null
Na & Nancy	10.1	7.82	Reject Null
Robert & Justin	16.7	7.82	Reject Null