Mitosis (Edexcel GCSE Biology: Combined Science)

• Mitosis is a nuclear division that gives rise to two genetically identical diploid daughter cells
  • In a human, this diploid number is 23 pairs of chromosomes

• All body cells (and not gametes) are produced by mitosis of the zygote
• Mitosis is required for:
  • Growth: mitosis produces new cells
  • Repair: to replace damaged or dead cells
  • Asexual reproduction: mitosis produces offspring that are genetically identical to the parent

The Cell Cycle

• There are 3 parts of the cell cycle
  • Interphase - Just before mitosis, the DNA in the nucleus copies itself exactly (forms x-shaped chromosomes)
  • Mitosis - Chromosomes line up along the centre of the cell where cell fibres pull them apart
  • Cytokinesis - The cell cytoplasm and membrane divides to produce two daughter cells; each new cell has a copy of each of the chromosomes

The three stages of the cell cycle

The Stages of Mitosis

• The process of mitosis is itself made up of a series of stages that begin after interphase has occurred. These stages occur in the following order:
  • Prophase - DNA condenses, chromosomes become visible and the nuclear membrane breaks down
  • Metaphase - Chromosomes line up on the equator of the cell (the metaphase plate)
  • Anaphase - Spindle fibres (also known as cell fibres) split the chromosomes down the centre and pull one chromatid to either side of the cell
  • Telophase - New membranes form around the chromosomes at either end of the cell

The stages of mitosis