Meiosis

• Meiosis


  A type of cell division that produces haploid gametes
• Prophase 1

  • Nuclear envelope breaks down
  • Chromatin condenses into chromosomes
  • Homologous chromosomes pair up and join at the place called chiasma becoming tetrads
  • Crossing over between homologous chromosomes occurs
• Metaphase 1


  Tetrads align at the equator, spindle fibres attached to each tetrad
• Anaphase 1


  Homologous chromosomes are separated and pulled to either side of the cell
• Telophase 1


  New nuclei form around the separated chromosomes. Cytokinesis follows through, splitting the cell into two haploid cells
• Prophase 2

  • Chromosomes condense again
  • Each chromosome consisting of two sister chromatids
• Metaphase 2


  Sister chromatids align at the equator of the cell, spindle fibres attached to each sister chromatid
• Anaphase 2


  Sister chromatids are separated again, forming chromosomes moving to either side of the cell
• Telophase 2


  New nuclei form around the separated chromosomes before cytokinesis follows through and splits each cell resulting in 4 non-identical daughter cells
• Crossing Over


  Exchange of DNA between homologous chromosomes to allow for genetic variation. This occurs during prophase 1.
• Independent Assortment


  Formation of random chromosome combinations to allow for genetic variation. This occurs during metaphase 1.
• Gametogenesis


  Following meiosis, the haploid cells further develop to become gametes; either sperm or eggs
• Non-Disjunction


  Chromosomes fail to separate during meiosis leading to abnormal number of chromosomes in cells. Usually occurs during Anaphase 1 or 2