Mitotic Index
Background
The mitotic index is the ratio between the number of cells in mitosis and the total number of cells
in a tissue sample. Mitotic indices are used as diagnostic tools in cancer treatment. Calculating
a mitotic index is as simple as counting the number of cells in the sample that are in mitosis and
also counting the total number of cells in the sample.
Part A. Calculating mitotic indices
Using the data below, determine the mitotic index of the samples collected in class using
prepared slides.
Plant Slides
Number of Cells
in Interphase
Number of Cells
in Mitosis
Mitotic Index =
# cells in mitosis
total # of cells
% Mitotic Index
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Part B. Comparing mitotic indices of normal and cancerous tissue samples.
Using the data below, determine the mitotic index of the various tissue samples, and answer the
questions that follow.
Tissue Type
Number of Cells
in Interphase
Number of Cells
in Mitosis
Normal Lung
19
1
Cancerous Lung
16
4
Normal Stomach
18
2
Cancerous
Stomach
14
6
Normal Ovarian
17
3
Cancerous
Ovarian
12
8
Analysis Questions
Mitotic Index =
# cells in mitosis
total # of cells
% Mitotic Index
1. Compare the mitotic indices that were calculated from the samples collected off of the
microscopes in class. Is this what you would expect? Why or why not?
2. Compare the mitotic indices of the normal tissue samples to the cancerous tissue samples
from the second data set.
3. What do the three cancer samples tell you about the growth rates of these types of cancer?
What implications might this have for screening, diagnosis, and treatment of these types of
cancers?