BIOLOGY

The cell division process produces new cells to replace older cells in the body. Somatic, or body, cells, like skin, hair, and muscle cells, divide during a process called mitosis. Mitotic division produces two cells that are identical to the parent cell. Human somatic cells go through the six phases of mitosis—interphase, prophase, metaphase, anaphase, telophase, and interphase.

Unlike somatic cells, the sex cells, sperm and egg, are produced during a process called meiosis. Meiotic division occurs in two stages—Meiosis I and Meiosis II. Meiosis I is quite similar to mitosis and results in two daughter cells. Unlike mitosis, though, the daughter cells from meiosis I are not exactly like the parent cell. In meiosis II the two cells from meiosis I divide and the overall result is four daughter cells, each of which contains only half the original number of chromosomes. During fertilization, an egg and sperm unite, resulting in a zygote that has the same number of chromosomes as the original parent cell. In this activity, you will explore and compare the phases of mitosis and meiosis.

• Push Pin

Part A Mitosis/Meiosis I

1. The first step of mitotic division is interphase. Click on the cell nucleus and observe what happens to the DNA in the nucleus (the red and blue strands) during interphase. Record brief observations in Data Table I. (Click on the table icon in the menu bar to access the table).
2. Now label the nucleus and nucleolus in the cell by dragging the appropriate pin over its corresponding cell structure. You must place each pin over the correct structure or it will not remain in place.
3. The second step of mitotic division is prophase. Click on the nucleus to see what happens during prophase. Record brief observations of prophase in Data Table I. Then use the appropriate pin to label a pair of sister chromatids, an example of spindle fibers and a centriole.
4. The third step of mitosis is metaphase. Click on the cell to see what happens during metaphase. Record brief observations in Data Table I.
5. The fourth step of mitotic division is anaphase. Click on the chromatids and record brief observations in Data Table I of what happens. Then use a pin to label one of the chromosomes.
6. The fifth step of mitotic division is telophase. Click on the pinched portion of the cell and watch what happens. Record brief observations in Data Table I.

Part B Meiosis II

1. The first step of meiosis II is interphase II. Click on the “Go to Part B” button on the last screen of Part A to see what the daughter cells from meiosis I look like in interphase II. Record brief observations in Data Table II.
2. The second step of meiosis II is prophase II. Click on either daughter cell to observe the changes in the cell during prophase II. Record brief observations in Data Table II.
3. The third step of meiosis II is metaphase II. Click on either cell to observe what happens during metaphase II. Record brief observations in Data Table II.
4. The fourth step in meiosis II is anaphase II. Click on either cell to observe the changes in the cell that occur during anaphase II. Record brief observations in Data Table II.
5. The fifth step of meiosis II is telophase II. Click on the pinched portion of one of the two cells and watch what happens to the cell during telophase II. Record brief observations in Data Table II.

The observations you recorded in this activity will help you answer the following questions.

1. In mitosis, during which step do the chromatids line up along the middle of the cell, followed by the spindle fibers extending from the centrioles to the chromatids?
2. In mitosis, what is the difference between the chromosomes at the end of prophase and the end of anaphase?
3. The DNA in a cell’s nucleus is copied to make to make two full sets of DNA in both mitosis and meiosis I. During what step does this happen?
4. How many daughter cells are produced by mitosis? By meiosis?
5. What is the purpose of each type of cell division?
6. A human somatic cell has 46 chromosomes. How many chromosomes are in daughter cell after mitosis? After meiosis?
7. Could two daughter cells that have been produced by mitosis fuse to form a zygote? Why or why not?
8. What is the function of the mitotic spindle?

1. metaphase
2. At the end of prophase, the chromosomes exist as paired sister chromatids. At the end of anaphase, the chromosomes are single.
3. interphase.
4. 2, 4
5. Mitosis produces cells for growth and repair. Meiosis produces gametes.
6. 46, 23
7. No. The zygote would have double the normal number of chromosomes.
8. To move the chromosomes during cell division.