Week 4 Midweek Assignment: Mitosis

Determining the Time Spent in Each Phase Using Whitefish Blastula

A prepared microscope slide of whitefish blastula cross-sections will show cells arrested in various stages of the cell cycle. (Note: It is not visually possible to separate the stages of interphase from each other, but the mitotic stages are readily identifiable.) If 100 cells are examined, the number of cells in each identifiable cell-cycle stage will give an estimate of the time it takes for the cell to complete that stage.

Given the events included in all of interphase and those that take place in each stage of mitosis, estimate the length of each stage based on a 24-hour cell cycle.

Background

Before you start this lab, you should read your materials in this section on the various phases. Additionally, the following YouTube video might be helpful as you watch an instructor identify cells in the various phases as he looks through a microscope.

mitosis – whitefish Blastula (05:56)

Finally, review
a close-up view of cells at various stages

Procedure

Examine the first image below, and then read the counting methodology.

Slowly scan the image below left to right, and up and down to view all the cells in the section. As you scan, you will notice that most of the cells are not undergoing mitosis but are in the interphase period of the cell cycle.

Practice identifying the cells in the image below before beginning the actual experiment.

The images below are of whitefish blastula in various stages mitosis. Before you count cells in the various phases, circle one example cell for each of the phases below and write the number next to the circle. You can draw the circle by selecting Draw in the Microsoft Word at the top and then selecting a pen.

Drawing Table

After you feel comfortable with your counting method and identifying cells in the various stages of mitosis, use the four images below of whitefish blastula to count the cells in each stage until you reach 100 total cells, recording your data below in Data Table 1. (You may not need to use all four images. Stop counting when you reach 100 total cells.)

After totaling the cells in each stage, calculate the percent of cells in each stage. (Divide total of stage by overall total of 100 and then multiply by 100 to obtain percentage.)

Data Table 1

To find the length of time whitefish blastula cells spend in each stage, multiply the percent (recorded as a decimal, in other words take the percent number and divide by 100) by 24 hours. (Example: If percent is 20%, then Time in Hours = .2 * 24 = 4.8) Record your data in Data Table 2.

Data Table 2

Conclusions

1. Drawing Table: Make sure you did the circle identifications with a number as mentioned with regards to the Drawing Table.

2. In your own words, explain the purpose of interphase.

3. In your own words, explain the purpose of mitosis.

4. Summary: Using complete sentences, write a summary of the results of the experiment. Be sure to talk about which ones seemed to be the faster and why that might be, and which are slower.

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