What is mitotic index and how do you calculate it

Virtual Lab: The Cell Cycle and Cancer

Worksheet

1. In which phase of mitosis do each of the following occur:

a. Centromeres split and chromosomes move toward opposite sides of the cell

b. Chromatin coils to form visible chromosomes

c. The nuclear membrane disappears

d. Sister chromatids line up in the center of the cell

2. In which phases of mitosis are sister chromatids visible, and attached to each other at the centromere?

Table 1: Record your data for the number of cells in each stage of the cell cycle observed in normal tissues.

Tissue Type

# Cells in Interphase

# Cells in Prophase

# Cells in

Metaphase

# Cells in Anaphase

# Cells in

Telophase

Lung Tissue

Sample 1

19

1

0

0

0

Lung Tissue

Sample 2

19

0

0

1

0

Stomach Tissue

Sample 1

16

1

1

0

2

Stomach Tissue

Sample 2

18

0

1

0

1

Ovarian Tissue

Sample 1

18

0

1

2

0

Ovarian Tissue

Sample 2

19

1

0

0

0

Table 2: Record your data for the number of cells in each stage of the cell cycle observed in cancerous tissues.

Tissue Type

# Cells in Interphase

# Cells in Prophase

# Cells in

Metaphase

# Cells in Anaphase

# Cells in

Telophase

Lung Tissue

Sample 1

16

0

2

1

1

Lung Tissue

Sample 2

15

1

3

0

1

Stomach Tissue

Sample 1

13

2

2

2

1

Stomach Tissue

Sample 2

14

2

1

1

2

Ovarian Tissue

Sample 1

11

2

2

3

2

Ovarian Tissue

Sample 2

12

2

1

2

3

Table 3: Use the data in Table 1 to calculate the Mitotic Index (average % cells dividing) for each normal tissue type.

Tissue Type

Avg. % cells at rest

Mitotic Index

Lung - normal

Stomach - normal

Ovary - normal

Table 4: Use the data in Table 2 to calculate the average % cells dividing and average % cells at rest in each cancerous tissue type.

Tissue Type

Avg. % cells at rest

Mitotic Index

Lung - cancerous

Stomach - cancerous

Ovary - cancerous

Questions:

3. What does your data indicate about the rate of cell division in cancerous tissue compared to the rate of cell division in normal tissue? What data did you use to answer this question?

4. Which type of cancer is the fastest growing? Explain your answer, using your relevant data.

5. With what you have observed in this lab, if you were to compare tissue sample from normal breast tissue and cancerous breast tissue:

a. Would you expect to see a difference in the rate of cell division in the cancerous breast tissue compared to the normal breast tissue? Explain your answer.

b. Could you make a prediction about the average % dividing cells in the cancerous breast tissue? Explain your answer.

6. Consider the % dividing cells in normal lung, normal stomach, and normal ovarian tissue. Why do you think there are more cells dividing in the stomach and ovary tissue than in the lung tissue?

7. This lab explores three common cancers. An additional form of cancer – Skin Cancer – used to be seen only in older individuals but is now seen in younger individuals, many in their early 20s. Skin cancer results from accumulated mutations to the DNA of skin cells, caused primarily by sun exposure. What factors do you think may be contributing to the increase in skin cancer among young adults?

Review:

1. Based on your data and observations, what are some of the differences between normal cells and cancer cells?

2. When studying cell division in tissue samples, scientists often calculate a mitotic index, which is the ratio of dividing cells to the total number of cells in the sample. Which type of tissue would have a higher mitotic index, normal tissue or cancerous tissue? Explain.

3. Different types of normal tissues in the human body have different mitotic indices. From the following list, which normal tissues would you expect to have the highest mitotic index: muscle, skin, kidney, or lung? Explain your answer.