SCIENCE - meiosis and mitosis

• Meiosis is the process by which sex cells (gametes) are produced from diploid parent cells, resulting in haploid gamete cells.
• Mitosis is the process by which cells divide to produce two identical daughter cells.
• Mitosis


  1. Cell nucleus divides into two new nuclei, each with the same number of chromosomes as the parent cell

  2. Occurs in body (somatic) cells
• Meiosis


  1. Single cell divides twice to produce four cells containing half the original amount of genetic information

  2. Produces sex cells - sperm in males, eggs in females
• Meiosis


  • The process that produces haploid gametes
  • A type of cell division in which the number of chromosomes is reduced by half
  • Occurs only in certain special cells of the organisms
  • During meiosis, homologous chromosomes separate, and the haploid cells that form have only one chromosome from each pair
  • Two cell divisions occur during meiosis, called meiosis I and meiosis II
• Meiosis I


  1. Prophase I: Nuclear envelope begins to break down, chromosomes condense, centrioles move to opposite poles, homologous chromosomes pair up

  2. Metaphase I: Spindle fibers attach to paired homologous chromosomes, which line up along the equator

  3. Anaphase I: Chromosomes of each homologous pair separate and move to opposite poles

  4. Telophase I and Cytokinesis: Spindle breaks down, new nuclear membranes form, cytoplasm divides, two haploid daughter cells result
• Meiosis II


  1. Prophase II: Nuclear envelope breaks down, spindle begins to form in each haploid daughter cell

  2. Metaphase II: Spindle fibers line up sister chromatids of each chromosome along the equator

  3. Anaphase II: Sister chromatids separate and move to opposite poles

  4. Telophase II and Cytokinesis: Spindle breaks down, new nuclear membranes form, cytoplasm divides, four haploid cells result
• • Cleavage furrow forms beginning the process of cytokinesis (cell division)
  • Resulting daughter cells are haploid (1N)
• Tension from spindle fibers aligns chromosomes at the metaphase plate