Exercise 2:  E-LAB-Mitosis and Meiosis

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Goals: To become familiar with the various stages in mitosis and meiosis and to understand the changes in chromosome number that occur during each of these forms of cell division.

Introduction:

Mitosis and meiosis are two forms of cell division in eukaryotic cells.  Mitosis is a form of cell division in which one cell (called the "parent cell") divides to produce two new cells (the "daughter cells") that have the same number of chromosomes as the parent cell.  Meiosis is a form of cell division in which each of the daughter cells of the division has one-half the number of chromosomes as the parent cell; meiosis occurs in the cells that, ultimately, will become the gametes (eggs or sperm) of the organism.

1.  Review mitosis using the animations at:

Your review of these animations should acquaint you with the four main phases of mitotic division:  prophase, metaphase, anaphase, and telophase.  Don't forget that, most of the time, the cell is engaged in interphase--the time period during which it is doing everything else a cell does except divide!

2.  Work through the Mitosis Simulation click-and-drag activity.

3.  Once you have completed the Mitosis Simulation, open a separate browser window by clicking on the little "ship's wheel" icon in the status bar, lower right.  From the new browser window, navigate to Blackboard and the E-LAB course homepage.  Click on the Course Documents button, open the Exercise 2 folder, then click on the "General Mitosis Orientation" selection to answer the review questions.  Answer the questions, being sure to click on the "submit answers" button when you are finished.  Leave this second browser window open while you work on the next section.

4.  After completing the General Mitosis Orientation, continue your work by studying mitosis in plant cells.  Review the background information on this topic in your lab manual.  Then, go to the second browser window and navigate to the "Plant Mitosis Orientation" to answer more questions about mitosis.  As you view the Plant Mitosis Orientation, keep in mind that you are viewing thumbnail images of onion root tips, including the cells that are dividing in those root tips.

5.  Now, go to the second browser window and select the "Root Tip Assignment."  Make a sketch of root tip cells in interphase and in each stage of mitosis.  Next, calculate the mitotic index of the cells in the root tip thumbnails.  To do so, first count 50 cells in the root tip and another 50 at the cut end of the root.  Determine whether each of these cells is in either mitosis or interphase, and record your counts in the table in the Root Tip Assignment and your lab manual.

1.  Review meiosis using the animations at:

2.  Work through the Meiosis I Simulation. Use the simulation to reinforce your understanding of nuclear disintegration and formation, chromosome condensation and movement, and cytoplasmic division through interphase and each of the four steps of meiosis I. Complete the same exercise for the second meiotic division in the Meiosis II Simulation.

3.  View slides of meiosis in plant cells by looking at the photos of pollen production in lilies at:

You should spend enough time with the pictures to recognize the different stages of both divisions.  Make sure you understand the role of meiosis in the life cycle of these organisms, and the role of each stage of meiosis in
reducing chromosome number.

4.  For slides of cells from different tissues, view the pictures and read the supporting material found at the following links:

You will not be asked for specifics from these pages, but you should study the pictures carefully enough to recognize cells in meiotic division. As above, be sure you understand the role of meiosis in the life cycle of various organisms.

5.  Go to the second browser window and navigate again to the Mitosis/Meiosis folder located under Course Documents. Select the link to the "Meiosis Simulation."  Complete this simulation.

6.  Now, choose one of the organisms you have studied in this section (Lily, Ascaris, or grasshopper). Sketch each stage of meiosis as indicated in your manual, then answer the questions from in the "Meiosis Slides Assignment," which is found on the same page, and in the second browser window, as the other "quizzes" you've already completed.