All copyrights reserved. This powerpoint is for a school project based on http://mset.rst2.edu/portfolios/a/abdelmessih_m/cellreproductio/home.htm

1. Cell division in Humans Mitosis and Meiosis…

2. Cell Cycle The cell cycle is the repeating set of events in the life of a cell. Cell division is one phase of this cycle of a cell’s lifetime. The other phase is called interphase and is divided into three stages: G1, G2, and S phase. The cell spends most of its life in interphase to prepare itself for cell division. If the cell is not a sex cell then mitosis occurs. If the cell is a reproductive one than it goes through meiosis.

3. Mitosis is the division of the nucleus and is a continuous process that allows for the organized distribution of a cell’s copied DNA to offspring. The process of mitosis is divided into four phases for easy understanding… Prophase, Metaphase, Anaphase, and Telophase and Cytokenis. Mitosis

4. Prophase The first stage of mitosis. It begins with the shortening and tight coiling of DNA into rod-shaped chromosomes. The copies of each chromosome stay connected to each other through a structure called centromere. The nucleus envelope begins to break down and disappear. Spindle fibers appear instead in preparation for metaphase.

5. Metaphase The second stage. During this phase the spindle fibers move the chromosomes to the center of the dividing cell or metaphase plate. Once in the center of the cell, each chromosome is held by those fibers.

6. Anaphase Third stage. Chromosomes separate at the centromere and move – centromere first, towards the opposite ends of the cell. After the chromosomes separate, they are considered individual chromosomes now.

7. Telophase and Cytokenisis These last two phases are the final stages of mitosis and considered to take place simultaneously. After the chromosomes reach the opposite poles of the cell the spindle fibers start to disassemble and chromosomes return to their less tightly coiled state. A nuclear envelope begins to appear around the chromosomes and a nucleus begins to form around the newly developing cell. In cytokenisis the cytoplasm divides also.

8. Meiosis The process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. This process is the formation of gametes which are haploid reproductive cells. Human gametes are sperm and egg cells. These cells also go through the cell cycle and therefore they begin meiosis with a duplicate set of chromosomes just as cells begin mitosis. Meiosis however, divide twice and therefore have two stages. The first cell division is called Meiosis I. and the second is Meiosis II. The Title above links a website with details of Meiosis.