Mitosis and Meiosis
To understand the cell cycle and mitosis and how these two processes function within an organism. To understand meiosis and how this process produces gametes.
All cells in your body complete a cell cycle in which they grow, divide and, eventually, die. The cell cycle consists of four phases: G1, S, G2, and M (Figure 1). Each phase is associated with a specific cellular function: typically growth, synthesis, and division. The G1, S, and G2 phases comprise a larger phase called interphase. During interphase, the cell grows and synthesizes (replicates) DNA in preparation for division. The G1 phase, also called Gap 1, is the first phase of interphase. During G1, the cell increases in size. The S phase, also called the synthesis phase, follows G1. During S phase, the cell synthesizes DNA. Each chromosome is now comprised of two identical sister chromatids as a result of DNA synthesis. The G2 phase, also called Gap 2, follows the S phase. During G2, the cell once again increases in size and produces proteins necessary for Mitosis. After G2, the cell is ready to begin the next phase in its life cycle, the mitotic phase.
Figure 1. The cell cycle.
Mitosis is a type of cell division process used by somatic cells. Somatic cells are all cell types excluding the germ cells, which produce gametes. Skin cells, liver cells, and brain cells are examples of somatic cells. Every cell in the human body, with the exception of gametes, contains 46 chromosomes. The number of chromosomes contained in each cell is called the diploid (2n) number. In humans, the diploid number is 46. Other organisms have different diploid numbers. For example, dogs have a diploid number of 78, guinea pigs have a diploid number of 64, and apples have a diploid number of 34. A somatic cell is always diploid, even after it divides.
Mitosis: 2n → 2n
Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase/ cytokinesis (Figure 2). Prophase is the first phase of mitosis. During prophase, the nuclear membrane begins to break down and the chromosomes condense and become visible under a microscope. Additionally, the centrosomes begin to migrate towards the poles of the cell. Metaphase is the second phase of mitosis. During metaphase, spindle fibers attach to the centromeres and pull the sister chromatids towards the metaphase plate. The sister chromatids are aligned along the metaphase plate in preparation for the next phase of mitosis, anaphase. During anaphase, the sister chromatids are separated from each other and pulled towards opposite ends of the cell. Once the sister chromatids are separated from each other, they are considered separate chromosomes and are called daughter chromosomes. Telophase/cytokinesis is the last phase of mitosis. During telophase/cytokinesis, the daughter chromosomes arrive at opposite poles of the cell and the nuclear membrane begins to form around the resulting daughter nuclei. Cytokinesis is the process of cytoplasm division that divides the parental cell into two identical daughter cells, each containing the exact chromosomal composition as the parent cell.
Figure 2. Mitosis in a somatic cell with a diploid number 2n = 4. Note that there are four chromosomes before mitosis begins, and each resulting daughter cell also has four chromosomes.
Part A: Simulation of Mitosis
Using the pop-bead chromosomes provided, simulate the stages of mitosis. Draw the stages of mitosis in the spaces provided. Using different colored pens or pencils will be helpful.
Part B: The Cell Cycle Game
In this computer game, you are a cell division engineer. You must help the cell complete interphase and mitosis. You will be given prompts along the way to assist you. Before attempting to play the game, please review the cell cycle process. If you make a...
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