Lab #1: Population Genetics by Julio Gonzalez, Lydia Mikhail, Mackenzie Whittall, and Zoe Du
Distribution of Genes in a Population
Hypothesis: The number of pairs of bean combinations when randomly picked out of a cup will match the Mendelian ratios found by punnett square.
Null Hypothesis: The number of pairs of bean combinations when randomly picked out of a cup will not match the Mendelian ratios found by punnett square.
Prediction: If we pick pairs of beans out of a cup randomly, then the number of pairs will not be similar to the Mendelian ratio.
Figure 1: Number of pairs of each combination of beans (heterozygous, homozygous white, homozygous speckled) we expected versus the number of pairs observed during the experiment.
Table 1. Chi-square calculations using our expected and observed bean pairs from our experiment.
Genotype
|
Observed
|
Expected
|
O-E
|
(O-E)2/E
|
Homozygous Speckled
|
13
|
12.5
|
0.5
|
0.02
|
Homozygous White
|
13
|
12.5
|
0.5
|
0.02
|
Heterozygous
|
24
|
25
|
-1
|
0.04
|
Total
|
50
|
50
|
Chi Square: 0.08
|
Degrees of Freedom: 3-1=2
Conclusion & Analysis:
From the data we collected as shown in Figure 1 and Table 1, we noticed that when there are
only two alleles, the results are very close to Mendelian genetics which in this situation would
suggest that there would be 12.5 pairs of 2 speckled beans or two white beans and 25 pairs
would have one of each bean. We observed that 13 pairs of speckled beans and 13 pairs of
white beans, as well as 24 pairs of beans were picked out of the cup during our experiment,
so therefore our data does not support our prediction that the results wouldn’t be close to the
Mendelian ratios. Using the chi squared value and degrees of freedom from table 1, we can find
a critical value of 5.99, which is much larger than our chi squared value which leads us to think
that in this situation shows mendelian genetics.
only two alleles, the results are very close to Mendelian genetics which in this situation would
suggest that there would be 12.5 pairs of 2 speckled beans or two white beans and 25 pairs
would have one of each bean. We observed that 13 pairs of speckled beans and 13 pairs of
white beans, as well as 24 pairs of beans were picked out of the cup during our experiment,
so therefore our data does not support our prediction that the results wouldn’t be close to the
Mendelian ratios. Using the chi squared value and degrees of freedom from table 1, we can find
a critical value of 5.99, which is much larger than our chi squared value which leads us to think
that in this situation shows mendelian genetics.
Genetic Drift or Natural Selection
Hypothesis: The population of generation one will not be the same as generation ten.
Null Hypothesis: The population of generation one will not be significantly different from generation ten because of the Hardy Weinberg equilibrium equation, which states that a the gene frequencies in a population remain constant from generation to generation.
Prediction: If we are randomly picking out beans without looking, then the variations of beans will not be equal throughout the generations.
Figure 2: Number of beans after ten generations for population A. While the speckled beans is continuously increasing, the red beans fluctuates. Both white and black beans gradually decrease.
Figure 3: Number of beans after 10 generations for population B. Red beans
continuously increases, while the white beans continuously decrease.
The black beans gradually decrease and the speckled beans fluctuate until
the fifth generation then increases.
Table 2. Chi-square calculations for Population A of our experiment.
Population A
|
Observed
|
Expected
|
O-E
|
(O-E)2/E
|
Red
|
14
|
24
|
-10
|
4.167
|
Black
|
0
|
4
|
-4
|
4
|
White
|
0
|
4
|
-4
|
4
|
Speckled
|
36
|
18
|
18
|
18
|
Total
|
50
|
50
|
Chi Square: 30.167
|
Degrees of Freedom: 4-1=3
Table 3. Chi-squared calculations for Population B of our experiment.
Population B
|
Observed
|
Expected
|
O-E
|
(O-E)2/E
|
Red
|
25
|
7
|
-18
|
46.286
|
Black
|
6
|
16
|
-10
|
6.25
|
White
|
0
|
15
|
-15
|
15
|
Speckled
|
19
|
14
|
5
|
1.786
|
Total
|
50
|
50
|
Chi Square: 69.322
|
Degrees of Freedom: 4-1=3
Conclusion/Analysis:
From the data we gathered represented in Figures 2 and 3, we observed that the populations
of both black and white beans decreased continuously; eventually, the amount of the white
beans became 0 in the tenth generation. On the contrary, the number of speckled beans and
red beans increased, though not at a constant rate. In the final generation, generation 10,
there were 36 speckled beans in Population A and 19 in Population B, while there were 14
red beans in Population A and 25 in Population B. After entering the laboratory and viewing
the 4 different beans (differing in size, structure and texture) we predicted that the allele
frequency change would gear toward the speckled beans (36 out of 50), since they are
the biggest and easiest to pick out of the cup. If the allele frequencies become less varied
(and move toward one allele) as the generations progress, then natural selection has occurred.
If the variation between the allele frequencies is consistently random, genetic drift instead has
happened. Due to the results we got in both populations, we confirmed our prediction that if
we are randomly picking bean pairs, then the variation of beans will not be equal throughout
the generations. In addition, the allele frequencies shifted greatly toward one allele which
eliminates any change of genetic drift being a possibility. We used p=0.05 for our chi-square
calculations and 3 for our degrees of freedom. We knew that our chi-squared value needed to
be less than 7.82 to fail and reject the null hypothesis, and since both of the chi-squared values
for Population A (30.167) and Population B (69.322) are tremendously larger than this value
(expected and observed allele frequencies were not close at all), we can safely reject the null
hypothesis. Essentially, generation one is the expected value while generation ten is the
observed one.
of both black and white beans decreased continuously; eventually, the amount of the white
beans became 0 in the tenth generation. On the contrary, the number of speckled beans and
red beans increased, though not at a constant rate. In the final generation, generation 10,
there were 36 speckled beans in Population A and 19 in Population B, while there were 14
red beans in Population A and 25 in Population B. After entering the laboratory and viewing
the 4 different beans (differing in size, structure and texture) we predicted that the allele
frequency change would gear toward the speckled beans (36 out of 50), since they are
the biggest and easiest to pick out of the cup. If the allele frequencies become less varied
(and move toward one allele) as the generations progress, then natural selection has occurred.
If the variation between the allele frequencies is consistently random, genetic drift instead has
happened. Due to the results we got in both populations, we confirmed our prediction that if
we are randomly picking bean pairs, then the variation of beans will not be equal throughout
the generations. In addition, the allele frequencies shifted greatly toward one allele which
eliminates any change of genetic drift being a possibility. We used p=0.05 for our chi-square
calculations and 3 for our degrees of freedom. We knew that our chi-squared value needed to
be less than 7.82 to fail and reject the null hypothesis, and since both of the chi-squared values
for Population A (30.167) and Population B (69.322) are tremendously larger than this value
(expected and observed allele frequencies were not close at all), we can safely reject the null
hypothesis. Essentially, generation one is the expected value while generation ten is the
observed one.
Hi, all!
ReplyDeleteYour group’s allele frequencies in population B had a very similar pattern to the alleles in my group’s population A, though ours was less extreme. After observing and evaluating these allele frequencies, it is evident that natural selection occurred in your population B. Even though the red alleles started with the lowest number in relation to the gene pool, after ten generations, the red allele was the most common in the population. This significant increase in the red allele indicates that the allele was more successful in the region that population B resided in after genetic drift occur. The significant decrease and eventual loss of the white allele indicates that the allele was not very fit for the environment. Additionally, I found it really interesting that the black and white alleles had the lowest allele frequencies in both your population A and population B after ten generations, regardless of the frequency during the first generation. This same observation was true for the allele frequencies in my group’s population A and B. The black and white alleles were either lost by the tenth generation or had very low allele frequencies. After glancing at a few other posts, this seemed to be a common pattern in most group’s populations. This possibly resulted from the fact that the black and white beans are a lot smaller in size than the red and speckled beans. Because of this, the black and white beans sunk to the bottom of the cup and were more difficult to grab when selecting the alleles for the following generation. I wonder how our results would have differed if we had used beans or beads of uniform sizes.
Great post. After seeing ur data table for your genetic drift and natural selection, I noticed that we both had no white and black beans left at the end but a lot of speckled beans. I believe that is because when picking out the beans, it is easier to take out the speckled ones than the other smaller ones. The Mendelian ratio doesn't work for these labs since there are some bias towards the bigger beans.
ReplyDeleteHi group,
ReplyDeleteIt’s interesting to see on your blog that the white beans in both of your populations extinct at almost the same generation, the 6th. I was surprised when I checked my group’s data and found that one of our populations had the same result, the white beans extinct at about the 6th generation. 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 white beans through generations as they were smaller than the other beans or beads, so the data turned out to be biased towards the large beads. It’s interesting too to see that the black and the red beads in your populations had different distribution curves on your graphs although they were approximately equal in size. Therefore, I wonder if there were any significant differences in the beads that would lead to these results. Great work guys!!
Hey everyone,
ReplyDeleteNice data! I think it's interesting that we had similar hypothesis and mostly similar data, but that your population B for part two had more black beans than what I expected to see. What was your method for selection? I was wondering if that might have played part in selection as well. We decided to use the forceps provided thinking it would create a more random effect, but I think that we still had the issue of small beans falling to the bottom and the forceps were better at grabbing bigger beans first. It makes me wonder how different results would have been if the beans were the same size, or if this was to make us more aware of dominant and recessive genes perhaps. Keep up the good work!
Hello Mackenzie, Julio, Zoe and Lydia,
ReplyDeleteI liked how clear your conclusions were, and how they were tied back to the Hypothesis and predictions very well. I found the genetic drift results in Part B interesting. At first, I also thought there was a bias in bean size as well. However, for your Part A, your group followed Medellin genetics as accurate as possible with the sample size. So overall, a spectacular job.
Hey guys,
ReplyDeleteI like the data a lot, especially the results for part B of the lab. I think both populations used in part B really represent what genetic drift can do, while it can maintain a balance in the allele frequencies it typically causes an alleles to decrease in frequency or disappear entirely from a population. For part A of the lab I was impressed with how close your results where with the expected.
Good day you guys, no surprise there in your Part A findings, that's just about if not exactly what our group got, my memory eludes me at the moment. Did you do anything to eliminate the problem that the beans were different sizes? Or did it just come out like that anyways?
ReplyDeleteCool beans. Your technique for picking beans from the cup was obviously superior to ours. we ended up with WAY more homozygous speckled because we used a spoon to pull out a few beans then shook the spoon a bit until one bean was left. the heavier speckled beans didn't fall off the spoon as easily as the lighter white beans. by the time we realized and changed tactics it was too late.
ReplyDelete