cell division

• Mitosis and Meiosis

  
• Mitosis


  Division of somatic (body) cells

  
• Meiosis


  Division of gametes (sex cells)
• Diploid (2n)


  Two of each type of chromosome (in homologous pair – carry the same trait)
• Haploid (n)


  One of each type of chromosome
• Human cells have 46 chromosomes
• The diploid number (2n) of chromosomes in humans is 46
• The haploid number (n) of chromosomes in humans is 23
• Reasons for mitosis


  • To replace/repair other cells that have been damaged or worn out
  • To allow multicellular organisms to grow & develop
  • For asexual reproduction (e.g. Binary Fission)
  • Because cells get too big (volume to surface area ratio)
• Reasons for meiosis


  • Meiosis results in four cells with half the number of chromosomes so that when the sex cells (sperm and egg) combine, the original or normal number of chromosomes will be restored

  
• Mitosis occurs in normal body cells (i.e. skin cells), and meiosis occurs in sex cells (i.e. sperm and egg) only

  
• Mitosis


  1. Interphase

  2. Prophase

  3. Metaphase

  4. Anaphase

  5. Telophase

  
• Interphase


  Cell preparing to divide, genetic material doubles

  
• Prophase


  • Chromosome pair up, chromosomes thicken and shorten, centrioles move to opposite sides of nucleus, nucleolus disappears, nuclear membrane disintegrates
• Meiosis produces 4 daughter cells, each with half the chromosomes of the parent
• Meiosis involves 2 cycles of cell division

  
• Mitosis produces two identical cells
• Mitosis does not bring genetic variety to a species

  
• The result of mitosis is two identical diploid cells
• The result of meiosis is four genetically different haploid cells