The stages of meiosis

• Meiosis


  A form of nuclear division that results in the production of haploid cells from diploid cells
• Meiosis


  • Produces gametes in plants and animals that are used in sexual reproduction
  • Has many similarities to mitosis however it has two divisions: meiosis I and meiosis II
  • Within each division there are the following stages: prophase, metaphase, anaphase and telophase
• Meiosis I


  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I
• Prophase I


  • DNA condenses and becomes visible as chromosomes
  • DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
  • The chromosomes are arranged side by side in homologous pairs
  • A pair of homologous chromosomes is called a bivalent
  • Crossing over of non-sister chromatids may occur at the chiasma
  • Centrioles migrate to opposite poles and the spindle is formed
  • The nuclear envelope breaks down and the nucleolus disintegrates
• Metaphase I


  • The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres
  • The maternal and paternal chromosomes in each pair position themselves independently of the others; this is independent assortment
• Anaphase I


  • The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle
  • The centromeres do not divide
• Telophase I


  • The chromosomes arrive at opposite poles
  • Spindle fibres start to break down
  • Nuclear envelopes form around the two groups of chromosomes and nucleoli reform
• Cytokinesis


  1. In animal cells: the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half

  2. In plant cells, vesicles from the Golgi apparatus gather along the equator of the spindle (the cell plate). The vesicles merge with each other to form the new cell surface membrane and also secrete a layer of calcium pectate which becomes the middle lamella. Layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell
• Meiosis II


  • There is no interphase between meiosis I and meiosis II so the DNA is not replicated
  • The second division of meiosis is almost identical to the stages of mitosis
• Meiosis II


  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II
• The end product of cytokinesis in meiosis I is two haploid cells
• Centromeres divide and individual chromatids are pulled to opposite poles in Anaphase II, creating four groups of chromosomes that have half the number of chromosomes compared to the original parent cell
• Nuclear membranes form around each group of chromosomes in Telophase II
• Cytokinesis in Meiosis II creates four haploid cells