Meiosis

• Meiosis


  The process of cell division that produces gametes (sex cells) with half the normal number of chromosomes
• Meiosis


  • Occurs in sex cells (gametes): egg and sperm
  • One cell becomes 4 NON-IDENTICAL cells
• Homologous chromosomes


  Chromosomes of the same length, with the same centromere position, and that carry genes that control the same inherited traits. One is from the mother, one is from the father.

  
• Haploid cell


  A cell with n chromosomes

  
• Diploid cell


  A cell that contains 2n chromosomes

  
• Meiosis I


  1. Interphase

  2. Prophase I

  3. Metaphase I

  4. Anaphase I

  5. Telophase I
• Meiosis II


  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II

  5. Cytokinesis
• Meiosis


  • Produces gametes to maintain the same number of chromosomes from generation to generation
  • When gametes combine in fertilization, the number of chromosomes is restored
• Meiosis consists of two sets of divisions
• Meiosis


  • Produces four haploid daughter cells that are not identical
  • Results in genetic variation
• Depending on how the chromosomes line up at the equator in meiosis


  Four gametes with four different combinations of chromosomes can result

  
• Genetic variation is also produced during crossing over and during fertilization


  When gametes randomly combine
• Mitosis and meiosis are compared
• Homologous chromosomes pair up during meiosis to exchange genetic material through crossing over.
• Meiotic prophase I is the longest phase, lasting about 12 hours.
• interphase


  chromosomes replicate

  chromatin condenses
• Prophase I


  Pairing of homologous chromosomes occurs. Each chromosome consists of two chromatids. The nuclear membrane breaks down.  Spindles form
• metaphase I


  Chromosome centromeres attach to spindle fibers.  Homologous chromosomes line up at the equator.
• anaphase I


   Homologous chromosomes separate and move to opposite poles of the cell.
• telophase I


  The spindles break down.  Chromosomes uncoil and form two nuclei.  The cell divides