Mitosis (Edexcel IGCSE Biology: Double Science)

• Mitosis is defined as nuclear division giving rise to genetically identical cells
• Mitosis is used for:
  • growth
  • repair of damaged tissues
  • replacement of cells
  • asexual reproduction 
• Most body cells have two copies of each chromosome
• We describe these cells as diploid
• When cells divide their chromosomes double beforehand (also known as duplication)
• This ensures that when the cell splits in two, each new cell still has two copies of each chromosome (is still diploid)

The process of mitosis

• Just before mitosis, each chromosome in the nucleus copies itself exactly (forms X-shaped chromosomes)
• Chromosomes then line up along the centre of the cell where cell fibres pull them apart
• The cell divides into two; each new cell has a copy of each of the chromosomes

The process of cell division by mitosis

• All cells in the body (excluding gametes) are produced by mitosis of the zygote
• Mitosis occurs during:
  • Growth: mitosis produces new cells
  • Repair: to replace damaged or dead cells
  • Asexual reproduction: mitosis produces offspring that are genetically identical to the parent
• Mitosis is important for replacing cells e.g, skin cells, and red blood cells, and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)