Meiosis and Fertilisation

• Meiosis


  The process by which gametes (sperm and egg cells) are produced, with half the normal number of chromosomes
• Chromosomes in normal human cells

  • 23 pairs
• Chromosomes in gametes


  • 23 single chromosomes
• Meiosis


  1. Chromosomes are copied

  2. Cell divides into two

  3. Cells divide one more time forming gametes
• Meiosis produces four gametes from one original cell, and each gamete is genetically different
• Fertilization


  The joining of a male gamete (sperm) and a female gamete (egg) to form a new cell with the full number of chromosomes
• After meiosis


  The number of chromosomes is halved
• After fertilization


  The full number of chromosomes is restored
• Human sperm cell and egg cell

  • Both have 23 single chromosomes
• Fertilized egg


  • Contains 23 chromosome pairs
• After fertilization


  1. The new cell divides by mitosis, producing a clump of identical cells (an embryo)

  2. As the embryo develops, the cells differentiate, forming different cell types