Lab #1: Cool Bean Population Genes by Darsi Fouillade, Mark Malabuen, Caleb Smith, and Lauryn Newman
Part A: Distribution of Genes in a Population
Hypothesis: When selected and paired together at random, sample alleles will produce a sequence
of genotypes consistent with mendelian ratios.
of genotypes consistent with mendelian ratios.
Prediction: Of the 50 bean pairs, 25% will be homozygous white, 25% will be homozygous speckled,
and 50% will be heterozygous.
and 50% will be heterozygous.
Data:
Figure 1. Genotype frequencies observed in the random pairing of model alleles (white beans and speckled beans).
Analysis: As our group’s chi-squared value of 10.24 exceeds the critical value of 5.99, we must reject
our null hypothesis and consider which factors other than chance may have played a role in our data
collection. Rather than the expected values of 12.5 homozygous white pairs, 12.5 homozygous speckled
pairs, and 25 heterozygous pairs—calculated according to mendelian ratios—our observed values—
shown in Figure 1—in both trials were each closer to ⅓ of the total pairs. Due to the absence of
alternative explanations, the most likely reason for the discrepancy between our expected and
observed results is human error in the randomization process used to select the bean pairs.
We failed to account for the perceptible difference in size and shape between the white and speckled
beans, so by selecting the beans by hand we may have allowed unconscious biases towards one
type of bean or the other to skew the pairing ratios towards homozygous genotypes and away from the
heterozygous genotype. Compiling the data from the entire lab section produced a chi-squared value
of 12.876, which is also greater than 5.99, indicating that other groups in the class likely made similar
mistakes. It may be beneficial for our group to repeat this experiment using a selection method which
eliminates the sense of touch as a factor in order to see if our data become closer to mendelian ratios.
our null hypothesis and consider which factors other than chance may have played a role in our data
collection. Rather than the expected values of 12.5 homozygous white pairs, 12.5 homozygous speckled
pairs, and 25 heterozygous pairs—calculated according to mendelian ratios—our observed values—
shown in Figure 1—in both trials were each closer to ⅓ of the total pairs. Due to the absence of
alternative explanations, the most likely reason for the discrepancy between our expected and
observed results is human error in the randomization process used to select the bean pairs.
We failed to account for the perceptible difference in size and shape between the white and speckled
beans, so by selecting the beans by hand we may have allowed unconscious biases towards one
type of bean or the other to skew the pairing ratios towards homozygous genotypes and away from the
heterozygous genotype. Compiling the data from the entire lab section produced a chi-squared value
of 12.876, which is also greater than 5.99, indicating that other groups in the class likely made similar
mistakes. It may be beneficial for our group to repeat this experiment using a selection method which
eliminates the sense of touch as a factor in order to see if our data become closer to mendelian ratios.
Part B: Genetic Drift or Natural Selection
Hypothesis: The null hypothesis is that the alleles will not be affected by genetic drift and will stay constant from G1 to G10. The alternative hypothesis is that genetic drift will change the frequency of alleles between G1 and G10.
Prediction: Random variations in frequency will occur to the model alleles in G10 compared to the frequencies observed in G1.
Data:
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Figure 2. Alleles in G2 of population A.
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Figure 3. Alleles in G10 of population A.
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Table 1. Numbers of model alleles (red beads, white beads, clear beads, and black beans) obtained after randomly dividing each population in half and doubling each allele to return it to its original size. Population A originally used 50 total alleles for each generation but all data from this population have been doubled to match the 100 total alleles used in population B.
Figure 4. The effect of random selection of alleles on relative allele frequencies in populations A and B over 10 generations.
Analysis: From the data shown in Figure 4, it would appear that both of the populations were affected
by genetic drift. Looking at it from a statistics angle, we calculated the chi-squared for both of the
population. Population A was 45.12 and Population B was 61.05. Since both of these values exceed
the critical value of 7.82, we can conclude that the null hypothesis can be rejected and that the
alternative hypothesis has been supported by these data. The variations in allele frequency observed
over these 10 generations in both populations are most likely due to genetic drift rather than natural
selection. Natural selection would require that some inherent characteristics of these alleles made them
more or less likely to be selected in each generation, and as we divided each population without looking
at or touching the beads and beans, it is highly unlikely that this was the case. Rather, it was simply
random chance that caused the black beans to be lost in population B and nearly lost in population A,
while the red beads drifted towards fixation in population A and the clear beads did the same in
population B. These results are consistent with the effects of genetic drift.
by genetic drift. Looking at it from a statistics angle, we calculated the chi-squared for both of the
population. Population A was 45.12 and Population B was 61.05. Since both of these values exceed
the critical value of 7.82, we can conclude that the null hypothesis can be rejected and that the
alternative hypothesis has been supported by these data. The variations in allele frequency observed
over these 10 generations in both populations are most likely due to genetic drift rather than natural
selection. Natural selection would require that some inherent characteristics of these alleles made them
more or less likely to be selected in each generation, and as we divided each population without looking
at or touching the beads and beans, it is highly unlikely that this was the case. Rather, it was simply
random chance that caused the black beans to be lost in population B and nearly lost in population A,
while the red beads drifted towards fixation in population A and the clear beads did the same in
population B. These results are consistent with the effects of genetic drift.
Great post! My partner and I also got the same results for the second experiment. However, since we used beans instead of beads, natural selection caused the change in the allele frequencies of the population. We think size matters in picking the individual beans because the bigger the beans, the easier to pick, increasing their frequencies in each generation. Your results are very interesting because the allele frequencies still changed even though the beads are all the same in size. How did you select your populations?
ReplyDeleteThe post was very clear and easy to follow. For part A, we got similar results. After looking at out results there was a bias towards the bigger bean (speckled), when selecting between the beans since it was easier to grab. In order to eliminate the bias, we decided to use gloves and a spoon. That is one suggestion, other wise nice post.
ReplyDeleteAwesome post guys, our data may be entirely different in terms of result but it's pretty interesting with the data and chi-squared value that you got. However as you mentioned, beans and beads are totally different feel when it comes to picking them for sure. But I also noticed that allele frequencies varies according to your data, there may have been slight error somewhere.. regardless of that you guys mentioned what have gone wrong and what it could've been if things were different and that justifies it!
ReplyDeleteI liked your post because it is short but concise. My group used the beans and one of the reason why we got our results was due to the size of the beans. I was curious to see how the lab would play out if they were all the same size and you guys did that, so that was cool. It was interesting to see that the two populations had the same trend of having one color over the others. The results from our lab weren't as different because we ended up with only two types of beans at the end. If we would have kept going, I'm sure we would have ended with just one type.
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ReplyDeleteHi, everyone! I enjoyed reading your results because they were very different from the results that my group ended up with. I found it interesting that in Population A, the red allele was twice as common as the other alleles, and over the ten generations, it continued to have a fairly steady increase in frequency. On the other hand, the black, clear, and white alleles became less common over time, and came close to being completely lost in the population. I wonder how many more generations it would have taken for Population A to completely lose the black, clear, and white alleles. I found it interesting how the black allele was almost lost in population A and completely lost in Population B, while in the allele that was headed toward fixation differed between the two populations. This makes your group’s results a great representation of genetic drift because the two sister populations evolved independently from one another. Your group’s results demonstrated that some alleles can follow similar patterns in the sister populations, while others could differ drastically.
ReplyDeleteHi group,
ReplyDeleteIt’s interesting to see on your blog that the clear beads extinct in population A, while the red beads had high-frequency distribution curve, although the clear and the red beads are supposed to have the same size. I was surprised when I saw your population B graph, as I saw the opposite; the red beads extinct, while the clear beads had high-frequency distribution curve. We all know that different ways of choosing the beans affect the allele frequencies of the genotypes. So, I wonder if my group had the same technique of choosing the beans like your group or not. It’s a little bit logic to lose the smaller beans through generations as they were smaller for our fingers compared to the large beads, so the data turned out to be biased towards the large beads. Therefore, it was confusing to see that the white and the red beads in your populations had different distribution curves on your graphs although they were approximately equal in size. So, I wonder if there were any significant differences in the beads that would lead to these results. Or there were some errors. Great work guys!!
I find the data your group presented is rather interesting. It would appear that other groups have similar results to the results you have in part B.
ReplyDeleteFor our experiment, my group worked with beans where the size really had an effect of how random our results were. It's interesting to read about an experiement that was essentially completely random (or as random as random gets for humans). Great work!
ReplyDeleteHi everyone! I really enjoy reading your post. In figure 2 , figure 3. and table 1, it is very interesting how the black allele eventually goes extinct. I also like how you guys include the analysis section.
ReplyDelete