Describe the specific events of mitosis

Mitosis I: Chromosome Replication and Movement

From Bio Lab Notebook

Objectives:

• Recognize and describe the major events of mitosis.
• Simulate chromosomal replication and movement during mitosis.
• Observe mitosis in onion root tips.

Part 1.  Describe the specific events of mitosis

In the spaces provided, list the events associated with each stage of mitosis. This list can serve as an excellent study guide, so be as complete as possible.

Table 1

Part 2.  Draw what is happening during each phase of mitosis. Make sure to include a nucleus (if present), and chromosomes, and centrioles.  Images of onion root tip cells undergoing mitosis can be found on the next page.

Interphase:                                                                             Prophase

Metaphase:                                                                            Anaphase:

Telophase:

Phases of mitosis in onion root tip cells

Interphase                                                   Early Prophase                             Mid Prophase

Metaphase                                              Anaphase                        Telophase

Figure 1. The phases of mitosis in onion cells

Part 3:  You will look at a microscope image of onion root tip cells and determine how long each phase happens by counting the number of cells in each phase. Then you will do a simple calculation to determine (roughly) how long each phase takes.

Examine the image of cells below.  For each of the cells in your sample, identify the stages of mitosis and place a mark in “Tally Marks” column of the Table provided below beside the appropriate phase. If you are unsure of the phases, refer to Fig. 1.

When you have classified each cell in your sample, count the tally marks for each phase and fill in the “Count” column. Of the cells you have counted, most of the cells are in which phase of mitosis? In other words, which phase of mitosis did you see/count the most?

Calculate the percentage of cells found in each phase. Divide the number of cells in a phase by the total number of cells in your sample, and multiply by 100. Enter this figure under the “Percentage” column of the Table.

The percentage of cells found in each phase is a measure of how long each phase lasts. For example, if 25 percent of the cells are in prophase, then prophase takes 25 percent of the total time for a cell to undergo mitosis. Mitosis in onion cells in onion cells takes about 960 minutes. Calculate the actual time for each phase using this information and the percentage you have just determined. Enter the time (in minutes) of each phase under the “Time (in minutes)” column of the Table.

Duration of phase (in minutes)  = percentage/100 x 960 minutes

Relative Duration of Each Phase of Mitosis

Part 4.  Questions

1. If a nucleus has six chromosomes during prophase, how many chromosomes does each cell have: (note: when do the chromosomes replicate? And when do they separate?)

during metaphase:                                          

during anaphase:                                            

Number of chromosomes per cell after mitosis is complete:                        

2. What region of a root has the most mitotic activity? Why?