Mitosis in an Onion Root KEY

Identify each stage of mitosis on the chart below and describe what you would expect to see.

Stage Distinguishing Characteristics
Interphase single, prominent nucleus
Prophase chromosomes visible
Metaphase chromosomes line up
Anaphase chromatids separate
Telophase two nuclei visible, cell splits


Procedure: You will be given a slide of Allium, which is an onion root tip. Growth occurs when cells divide, so the root tips should have several cells in the process of cell division. View the root tip under the microscope and search for organized blocks of cells where nuclei are plainly visible. (Most activity will be occurring at the tip of the root). Move the slide around until you find a good spot that shows the cells in various stages of mitosis. *Make-Up work, see Mitosis in an Onion Root makeup

Stage Sketch Estimated Number of Cells
Interphase Answers vary, the majority of cells are in interphase, but you can usually find one or two in the other stages.
Prophase
Metaphase
Anaphase
Telophase

Analysis

1. Why is the onion root a good specimen for studying mitosis?

Cells of the onion are growing so it is easy to find cells in various stages of mitosis.

2. The majority of the cells in your specimen were in which stage of the cell cycle? interphase

3. In allium, interphase lasts about 15 hours, and mitosis takes up 80 minutes. Assuming that each stage of mitosis takes the same amount of time, how many hours old is a cell that is just starting anaphase. (Yes, you'll need to do some algebra here - show your work) 80 minutes means that each of the four stages (PMAT) takes 20 minutes. When a cell is just starting anaphase, it has already gone through prophase and metaphase, so it is 40 minutes old

4. Sketch one cell in any stage of mitosis. Label the stage and label any cell structures that are visible. The spindle fibers and chromosomes should be visible.

There are many pictures of cell mitosis at http://commons.wikimedia.org/wiki/Mitosis, generally students will have simple drawings, just look for the main ideas being depicted.

5. Which stage of mitosis is the easiest (in your opinion) to see on the slide? What about it makes it easy to identify? answers vary, metaphase is usually pretty obvious