Lab 1: Population Genetics By Deborah and Helen
Assignment 1 Majors Animal Biology Winter 2018
BIOL& 212 Lab
1: post-lab assignment - Population Genetics POPGEN-B
Group
Members: Deborah Haney, Helen
(Shuaiqian Men)
A. Distribution
of Genes in a Population
Hypothesis:
Without environmental pressure, the frequency of equally dominant alleles in a
population will be equal.
Prediction: In
our population of 50 individuals, each with two beans, and 3 possible genotypes
(speckled-speckled (p^2), speckled-white (pq), and white-white (q^2)), each
genotype will be in line with Mendelian genetics (25% p^2, 50% pq, 25% q^2).
Conclusion: We
made 2 mistakes here: First, we had 2 bags of beans (1 bag speckled and 1 bag
of white), and we didn’t know how many beans were in each. We should have
counted out 50 of each bean but instead we poured all the beans in the cup.
Second, we noticed that our method of pulling beans out on a plastic spoon and
shaking it until there was only 1 bean resulted in the smaller white beans
being tossed and heavily affected our results. With these mistakes, I would
consider these results invalid. By the way, the chi-square of the results is 18
(calculation is shown in Table 1).
Such large number also represents that our results fail to support the
hypothesis.
Table
1: Calculate the Chi-Square of the data in Figure 1
|
||||
Expected
|
Observed
|
O-E
|
Chi-Square=(O-E)^2/E
|
|
Homo White
|
12.5
|
5
|
-7.5
|
56.25/12.5=4.5
|
Heter
|
25
|
20
|
-5
|
25/25=1
|
Homo Speckled
|
12.5
|
25
|
12.5
|
156.25/12.5=12.5
|
Total
|
18
|
|||
B.
Genetic Drift or Natural Selection
Hypothesis:
Without the environmental pressure, the frequency
of phenotypes in a population will be equal.
Prediction:
Our 4 “alleles” will be in the same
proportions in generation 10 as generation 0.
Table
2: Generations (Population B)
|
||||||||||
“Allele”
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
Red
|
24
|
28
|
30
|
34
|
38
|
32
|
26
|
24
|
22
|
24
|
Clear
|
24
|
24
|
24
|
18
|
12
|
20
|
26
|
24
|
24
|
22
|
Navy
|
20
|
20
|
14
|
12
|
16
|
14
|
16
|
20
|
24
|
28
|
White
|
32
|
28
|
32
|
36
|
34
|
34
|
32
|
32
|
30
|
26
|
Conclusion: Generation 0 had 25 beads of each of the
four colors, so for our null hypothesis and prediction to be confirmed,
generation 10 would also have to have 25 of each color. Generation 10 was very
close to generation 0 (within 3 beads) so we can safely confirm our hypothesis.
I believe our methods were sound in this case. By the way, the chi-square for
this test is 0.8 (calculation is shown in Table
3) which is fit enough to support that our results are in line with the
hypothesis.
Table
3: Calculate the Chi-Square of the data in Figure 3
|
||||
Expected
|
Observed
|
O-E
|
Chi-Square=(O-E)^2/E
|
|
Red
|
25
|
24
|
-1
|
1/25=0.04
|
Clear
|
25
|
22
|
-3
|
9/25=0.36
|
Navy
|
25
|
28
|
3
|
9/25=0.36
|
White
|
25
|
26
|
1
|
1/25=0.04
|
Total
|
0.8
|
|||
Great post! I got opposite results from yours for both experiments. My partner and I used beans for the second experiment and thought the difference in the allele frequencies was due to the different sizes of the beans and your results confirmed our prediction. It's also interesting how the beads frequencies went up and down in between the 1st and 10th generation, but still resulted in similar frequencies in the end (Figure 2). By the way your method to pick the beans in the first experiment is very creative.
ReplyDeleteI find that kind of interesting that you got similar distributions from gen 1 and gen 10. For a lot of people, including my group, there was usually a dominant allele at the end but overall your gen 1 and gen 10 were pretty balanced. Overall I like you post and the work here is A-Okay!
ReplyDeleteNice post. I noticed that your end results in population B were very close to your starting number of alleles. My group had different results, 2 of our alleles were lost from the population. We used beans for our experiment and believed natural selection occurred. Our data shows that bigger beans had a better chance of surviving. Your experiment looks more like genetic drift; you used beads, which would make the process more random. (since the beads are the exact same texture and size.) Once again great post.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteI am surprised you guys had so many heterogeneous combinations because for my group, we had very little due to the size difference in beans causing us to first pick the large speckled ones then the small white ones. It is also very interesting that the clear and navy beads nearly died out near the middle generations but were able to make a come back. his really shows that although there may be very few of an allele left, there is still a chance for them to come back. I think you guys did a good job in explaining why the results you obtaining in the first part of the experiment, but I think you guys should have used the calculations for the chi-squared to farther support your reasoning instead of adding it as a by the way or an after thought. This applies to both parts of the experiment. In addition, you guys should have added in your critical value in order to explain why you results were invalid, instead of saying just your chi-square value and saying it does not support the Mendelian Genetics. I like how you included a table of your data instead of just the graph because it makes it easier for the viewers to see the numbers you obtained. Although in my opinion you should have picked a graph without vertical lines going through each point. It takes up too much space making the graph look messy and harder to read. In addition, I think you should focus on being more clear in your captions. Some of the figure captions are too wordy and should instead be more to the point.
ReplyDeleteIt's interesting to see that you got more homo speckled than what you expected, almost double. It's opposite to our data, our observed and expected were very close, 22-25. For population B, I see that your data showed all the populations were very close. The white and red were increased around generation 3-7, you expected more than what you observed. On another hand, the blue and clear were decreased from generation 3-7, and you observed more than what you expected. It's also interesting to look at the ch-square table, and the observed and expected values were very close. The results were very similar at the end base on the Chi-square table. Anyway, good job on your post.
ReplyDeleteIt is a nice post for your lab. By including your reflection on the potential error of the experiment, the careful thinking in writing the post is seen. Based on the hypothesis of the experiment in part A, as a viewer, I understand the reason behind your decision of denying the result which is definitely not the easiest decision to do. Also, I like the captions of the graph since I thought it was only another place to put the title.
ReplyDelete