Investigation: Level 3

Bean Population Genetics


Experiment #1: The purpose of the first experiment is to demonstrate genetic drift. It was suppose to show us genetic drift by showing us the effects of taking a small number of different beans and using them to form the next generation. This showed us that as the population of a certain gene got smaller, it was harder for it to reproduce. This means that the gene that wasn't reproducing would eventually die off and the other would thrive.

Experiment #2: The purpose of this experiment is to demonstrate natural selection. To do this we used a paper plate with holes randomly poked through the plate. The paper plate is a factor of the environment. Since the beans are not the same size, one type of beans will fall through the plate more often than the other. The beans that fall through the plate is the new gene frequency of the next generation.

Procedures for Experiment #1:

1. Get red beans and white beans and separate them into 9 cups: the 1st cup with 90 red and 10 white, 2nd cup with 80 red and 20 white, 3rd with 70 red and 30 white, etc.

2. Either scoop or shake out 5 beans randomly from the 50R/50W cup. Determine the gene frequency of the new population.

3. Find the cup with the same frequency of the new population and repeat the same step.

4. Then do the same steps until the 10 generations (trials) are done or the gene frequency reaches fixation.

5. After that trial is done, have another group member do this again.

6. Do the same steps four more times but the first 2 times scoop or shake out 10 beans and the other 2 times scoop or shake out 20 beans.

Procedures for Experiment #2:

1. Use the same cups, with beans, as in experiment #1.

2. Pour beans out of the 50R/50W cup onto the paper plate, with holes, until the correction sample size population falls through the plate (either 5, 10, or 20). If too many fall through then the trial must be repeated.

3. Repeat as in Experiment #1, so that there are 2 experiments for each population size (5, 10, 20). Do this until you reach fixation or 10 trials.

Experiment #1: In the first trial of our first experiment (sample size of 5), our new gene population frequency was .6, or 60%, that was red. The second generation (trial) was also 60% red. The third generation was 100% red. As the population of the white beans shrunk, there was less of a chance that the white beans would reproduce. So eventually the white beans, which are and example of alleles, would die off and be gone forever.  In the rest of our experiments, the red beans always reached fixation.

Experiment #2: In the first trial of our first experiment, our new gene population was a fixation of white beans. This happened with all our experiments in the first trial except the fifth experiment where the first generation was .8, or 80%, white. The second generation was a 100% white.

Sample size:

The sample size of the experiments affected the outcome. The bigger the sample size the the more detailed the experiments were. We were able to get a more specific gene frequency of the beans when we used a sample size of 20 instead of 5. In one of the sample sizes of 5 (in Experiment #1) we only did 3 trials, however, when we used a sample size of 20, we did 7 trials (generations). This allowed us to get a more detailed look at what might happen to a certain population. In Experiment #2, almost all our experiments took 1 generation to become a fixation of white except for one of the experiments with a sample size of 20.


In Experiment #1 , the red beans always ended up becoming the only allele left in the population. However, in Experiment #2 white always reached fixation. Both experiments were similar in how the sample size affected the outcome of the experiment. Usually, the bigger the sample size the more generations it took to reach fixation. This happened more with Experiment #1 than Experiment #2. Usually in Experiment #1, it took more generations for a certain gene to reach fixation than in Experiment #2.


Genetic drift is a random change in population that influences the gene frequency. Natural selection also is a change in population that influence the gene frequency, however it is influenced by the environment. Genetic drift is when there is less variations or biodiversity in. In natural selection, the alleles that are chosen are affected by the environments conditions. The gene frequency of the alleles for genetic drift is a random chance of what alleles become the new generation. The environment conditions, biodiversity, and variations affect the gene frequency of the alleles in natural selection. Genetic drift affects the amount of biodiversity and variation there is in a population.  

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