AP Biology: Notes and Practice
Chi-Square Practice Problem - The Effect of Cancer on the Timing of Mitosis
For the following problem, identify the hypothesis you are testing, state the null hypothesis,
show your work in calculating the Chi-square value, identify the degrees of freedom, and
indicate whether you will reject or accept (fail to reject) your null hypothesis.
Critical values of the Chi-Square distribution
Probability (p)
Degrees of Freedom (df)
1
2
3
4
5
0.05
3.84
5.99
7.82
9.49
11.1
0.01
6.64
9.21
11.3
13.2
15.1
0.001
10.8
13.8
16.3
18.5
10.5
A scientist is interested in determining whether the timing of mitosis is different in healthy and
cancerous cells. The following information is collected.
Table 1: Mitosis in Normal Chicken
Stomach Cells
Stage of
Total # of
Mitosis
cells
Table 2: Mitosis in Cancer Chicken
Stomach Cells
Stage of
Total # of
Mitosis
cells
Interphase
440
Interphase
416
Prophase
40
Prophase
54
Metaphase
8
Metaphase
15
Anaphase
2
Anaphase
3
Telophase
10
Telophase
12
TOTALS
500
TOTALS
500
AP Biology: Notes and Practice
1. Formulate null hypothesis for the question below:
Is there a statistically significant difference in the timing of mitosis in healthy and cancerous
cells based on the number of cells in each phase of mitosis?
2. When using Chi Square Analysis to evaluate experimental data, the “observed” and
“expected” values used are from the experimental and control groups, respectively. Why is
this logical?
3. Calculate the Chi Square value for this data. Show all of your work:
4. What conclusion can you draw based on the Χ2 value calculated in question 2? Explain your
reasoning.
5. Observing the data in tables 1 and 2, what conclusion can you draw regarding how cancer
affects the time a cell spends interphase and mitosis? Explain your reasoning.
6. Cancer cells typically contain DNA that was poorly copied from the parent cell and contains
many errors. Based on your answer to the previous question, why might this be true?