Lab 1: Natural Selection and Genetic Drift

Evolution Lab 1:
Pinto Beanboozled!

Bio Squad
Matthew Donnelly, Bailey Longoni, Aaron Oberstadt, EJ Tilt

What would happen if 4 types of beans were taken from a cup, each type doubled, and the total were halved, over and over? Evolution operates by similar means, through random reproduction and random selection for generations on end. But is this an actually random process? And if not, what happens to such a population over time?

Hypotheses

We hypothesized that random selection of four different types of beans over the course of ten generations would lead to a statistically significant change in frequency in the type of bean selected; this is because natural selection will favor certain bean types over others. Our prediction under the conditions of this hypothesis is that speckled beans are more likely to be selected for because their larger size makes it easier to be picked up. Therefore, speckled beans will have a large increase in allele frequency.

To accurately test for this, we tested a null hypothesis, which stated that the frequency at which each bean is selected will not change significantly over time.

Figure 1.

10 generations of bean population A and the number of circle, speckled, black, and white beans during each generation. The speckled bean frequency increased to 50 of 50 in the 9th generation, accompanying the elimination of the other three beans from the population.

Figure 2.

10 generations of bean population B and the number of circle, speckled, black and white beans in each generation. The frequency of speckled beans increased to 47 of 50 at generation 10 while each other bean type was reduced to 1 of 50.

Conclusions

As seen in figures 1 and 2, there was a significant change in bean frequency from generation 1 to generation 10, demonstrating a change of allele frequency. Our data supported our hypothesis that random selection of the beans resulted in a change in allele frequency due to traits, and also supported our prediction that the speckled bean would become the dominant allele in these populations, suggesting the work of natural selection. We believe that because the speckled bean was bigger, it was easier to pick out of the cup and also rose to the top of the pile of beans.

The chi-squared value for our first data set is 88.275, and the chi-squared value for our second data set is 200. These are much larger than the critical values necessary for these results to be accepted as not random; therefore, we reject our null hypothesis. The random selection of four different types of beans over 10 generations did lead to a statistically significant change in frequency of the type of bean selected, and it is likely due to natural selection of the speckled beans.