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Mitosis and Meiosis Mitosis: Cell Division In each human cell there are 23 unique chromosomes each containing thousands of genes. Most cells in the human body have 2 copies of every chromosome These cells are called diploid (2n). Mitosis In order to keep the same genetic information cells undergo a process of division that ensures the same information is passed from parent to offspring. A) Cell Cycle A) Cell Cycle The life cycle of a cell has 2 portions: Interphase and Mitosis. Interphase is the normal condition of a cell. During this time the cell does its job and prepares for division. Mitosis is the process of division. A) Cell Cycle Interphase has 3 steps: G1- The cell produces proteins and performs its normal functions in the body. S – DNA inside the nucleus replicates. G2 – The cell resumes growth/function and readies for division. B) Mitosis Mitosis is divided into 4 steps: Prophase Metaphase Anaphase Telophase After Mitosis Cytokinesis occurs, which is the division of the cytoplasm. Mitosis: Prophase The nuclear envelop breaks down Chromatin condenses into chromosomes (Xs) Spindle fibers begin migrating to opposite ends. Mitosis: Metaphase The individual chromosomes line up at the center metaphase plate Centrioles and spindles are at opposite ends of the cell and connected to every pair of chromosomes at the centromere. B) Mitosis: Anaphase The centrioles pull on the spindles and separate the chromatids to opposite sides. B) Mitosis: Telophase The chromatids are now in opposite ends of the cell and they begin to decondense. Nuclear membrane begins to reform. Spindles break down. B) Mitosis: Cytokinesis In animals proteins pinch off the center of the cell into 2 each parts, seperating the cytoplasm. In plants the Golgi synthesizes a new cell wall along the metaphase plate, creating 2 separate cells. C) Meiosis In sex cells cell division is different. The process must half the number of chomosomes in each cell. This allows for fertilization to recreate the complete number of chromosomes. C) Meiosis The process of meiosis is called a reduction division. There are 2 rounds of division with some slight differences. C) Meiosis C) Meiosis The first round of meiosis has the following steps: Prophase I, Metaphase I, Anaphase I, and Telophase I. The second round of division is made up of: Prophase 2, Metaphase II, Anaphase 2, and Telophase 2. C) Meiosis Differences: During Prophase I homologous chromosomes pair up at the metaphase plate! There is NO DNA duplication between Meiosis I and II, so the DNA never has a chance to double. The end result is 4 haploid cells instead of 2 diploid cells. C) Meiosis