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. This process produces four cells, but unlike mitosis, the four cells are not exactly like the parent cell. Daughter cells created in meiosis contain 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 their parent cells. 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.
2. The second step of mitotic division is Prophase. Place the pushpin on the appropriate structure in the cell to identify the chromatids, spindle fibers, and centriole.
3. The third step of mitotic division is Metaphase. Place the pushpin on the appropriate structure in the cell to label the chromosomes.
4. The fourth step of mitotic division is Anaphase. Click on the chromatids and observe what happens in the cell.
5. The fifth step of mitotic division is Telophase. Click on the pinched portion of the cell and observe.

Part B Meiosis II

1. The first stage of meiosis (Meiosi follows the same steps as mitosis. However, meiosis occurs in two stages. The first step of the second stage of meiotic division is Interphase II. Click on the cells and observe what happens.
2. The second step of the second stage of meiotic division is Prophase II. Place the pushpin on the appropriate structure in the cell to identify the chromatids, spindle fibers, and centriole.
3. The third step of the second stage of meiotic division is Metaphase II. Place the pushpin on the appropriate structure in the cell to identify the chromosomes.
4. The fourth step of the second stage of meiotic division is Anaphase II. Click on the chromatids and observe what happens in the cell.
5. The fifth step of the second stage of meiot division is Telophase II. Click on the pinched portion of one of the two cells to divide the cell into four cells.

1. How many daughter cells are produced during mitosis? How many are produced in meiosis?
2. A human somatic cell contains 46 chromosomes. How many chromosomes are in each daughter cell after mitosis? How many chromosomes are in each daughter cell after meiosis?
3. What is the purpose of each type of cell division?
4. Why must the chromosome number be reduced by half in meiosis?
5. What is the function of the mitotic spindle? When does it appear? When does it disappear?

1. 2, 4
2. 46, 23
3. Mitosis produces cells for growth and repair. Meiosis produces gametes.
4. The chromosome number must be reduced by half so that when egg and sperm fuse, the zygote will have the correct number of chromosomes.
5. The mitotic spindle moves chromosomes during cell division. It appears in prophase and disappears after telophase.