Assume you are Gregor Mendel and have performed one of his pea plant experiments. You conduct a dihybrid
cross with two heterozygotes (RrYy) for the genes of texture and color. Round peas (R) are dominant to wrinkled
peas (r) and yellow peas (Y) are dominant to green peas (y). You are testing to see whether the observed
phenotypic ratio of peas matches the expected. (Hint: This is very similar to what we did in Lab 9!).
1. What are the null (H0) and alternate (HA) hypotheses for this experiment? (5 pts)
a. H0: The observed values are not going to stray too far from the experiment ratio
b. HA: The observed values are going to stray too far from the experiment ratio
2. Complete the table below, assuming you’ve counted the number of peas indicated: (8 pts)
Observed
Expected
O–E
(O – E)2
!
(O – E)2
E
Smooth, Yellow
549
579.375
-30.375
922.64
1.592
Smooth, Green
198
193.125
4.875
23.77
0.1231
Wrinkled, Yellow
213
193.125
19.875
395.02
2.045
Wrinkled, Green
70
64.375
5.625
31.641
0.4915
Total
1030
1030
3. What is the X2 value (X2CALC): 4.2516 (2pts)
4. Using the table below, and a significance level of 0.05, what is the X2 critical value (X2CRIT)? 7.815
2pts)
Significance Level (α-level)
df
0.50
0.10
0.05
0.02
0.01
0.001
2
1.386
4.605
5.991
7.824
9.210
13.815
3
2.366
6.251
7.815
9.837
11.345
16.268
4
3.357
7.779
9.488
11.668
13.277
18.465
5
4.351
9.236
11.070
13.388
15.086
20.517
5. Based on your results, do you accept or reject the null hypothesis (H0)? (2pts)
We fail to reject the null
6. Why? (3pts)
The Chi-squared value is lower the the critical value thus the observed values wont stray too far.
7. What is the biological meaning behind these results (what can you say about the observed
phenotypic ratio)? (3pts)
The observed values are not going to stray too far from the experiment ratio because of Mendels Law