Biocraft Level 3:
Investigating Genetic Drift

Founder Effect

Bottleneck Effect

Bean Bag Population Genetics

a.) The purpose of this experiment was to compare natural selection and genetic drift. During the experiment, students discovered various patterns, trends, and relationships. In order to understand genetic drift (experiment #1), the students began with a selection of red and white beans (a total of 100 beans; 1:1 ratio). He or she then randomly spooned five beans out of the cup and into a bowl. The resulting ratio was then used for the next trial. For example: if there were two white and three red, the ratio would be 2:3 (40 white and 60 red). This process is repeated until all five beans are one color. This is done a total of two times with five, ten, and twenty randomly selected beans. To demonstrate natural selection (experiment #2), a filter (plate with holes large enough for the beans to fall through) was used instead of a spoon, but otherwise, the procedures were identical.

b.) Many qualitative and quantitative similarities and differences were noticed while practicing this experiment. In the experiment demonstrating genetic drift, the majority of the trials resulted in the elimination of white beans, but the opposite was true for the results of the experiment demonstrating natural selection, for the majority of the results showed the elimination of the red beans. Also, there was no specific pattern for the second experiment, averaging at four tests. However, the first took more trials to complete when tested on a larger population. In conclusion, population size did not affect natural selection (because it acts on a phenotype), but did affect genetic drift (because it acts on the genotype.

c.) Sample size/population only affects genetic drift because natural selection is not random and acts on the phenotype. The number of organisms does not account for their survival because it does not make a difference in their fitness to the environment. For more examples, see above.

d.) The outcomes of the two experiments both result in the elimination of a certain trait/species. There is no pattern in natural selection, but genetic drift becomes a longer, more complicated process the bigger the population size. Another contributing factor to the contrasts of the two is because natural selection acts on the phenotype (not random), but genetic drift acts on the genotype (random).

e.) Genetic drift reduces biodiversity and genetic variation. This causes more mutations due to the fact that there are less genes to be rearranged when organisms reproduce. Because of the decreased biodiversity, the amount of different species becomes less and less, meaning that if one goes extinct, it will drastically affect the environment, population, and ecosystem. Natural selection also decreases biodiversity and variation, but only eliminates those that are not fit and would not live anyway. This allows species to survive and efficiently thrive. If one goes extinct, the majority of the remaining organisms will adapt to fit their environment and continue to reproduce. The environment plays an important role in both of these natural processes. In natural selection, organisms must adapt for fitness, while in genetic drift, it causes random changes to the size in the population.