Meiosis

• Meiosis


  A double reduction cell division where 1 germline cell undergoes 2 rounds of cell division to produce 4 daughter cells
• Resulting 4 daughter cells are genetically unique with half of the chromosomes as the parent germline cell
• Daughter cells


  Called gametes, which include sperm and egg cells
• Gametes are used for sexual reproduction
• Gametes


  • Sperm
  • Egg cells
• Gametes have only half the number of chromosomes compared with somatic cells
• Haploid


  Cells with half the number of chromosomes (n)
• Diploid cells = 2n e.g. humans = 2 x 23 pairs = 46 total chromosomes
• Haploid cells = n e.g. humans = 23 chromosomes per gamete
• Steps of Meiosis


  1. Meiosis I: Separates homologous chromosomes into 2 different cells

  2. Meiosis II: Separates sister chromatids into 4 different cells
• Meiosis terminology


  Uses the same terminology as mitosis e.g. Metaphase I and Metaphase II
• Genetic Diversity 1: Crossing over


  Formation of new recombinant chromatids by swapping with a homologous chromosome pair
• Recombinant chromatids exchange genes to create diversity as they are no longer identical
• Genetic Diversity 2: Independent assortment


  At metaphase II, homologous chromosomes line up randomly at the centre of the equator and move to either pole
• Random positioning means there are different ways in which chromosomes will separate