Meiosis (Edexcel IGCSE Biology: Double Science)

• Meiosis is a type of nuclear division that gives rise to cells that are genetically different
• During meiosis, the number of chromosomes must be halved to form the new cells; these new cells are called gametes (sex cells)
  • We describe gametes as being haploid - having half the normal number of chromosomes
  • There would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg) if this did not happen
• Meiosis is important for
  • The production of gametes e.g. sperm cells and egg cells, pollen grains and ovum
  • Increasing genetic variation of offspring

The process of meiosis

• Meiosis starts with chromosomes doubling themselves, as in mitosis, and lining up in the centre of the cell
• After this has happened the cells divide twice so that only one copy of each chromosome passes to each gamete
  • First division: chromosomes pair up along the centre of the cell, then cell fibres will pull the pairs apart, and each new cell will have one chromosome pair
  • Second division: chromosomes will line up along the centre of these cells, and cell fibres will pull them apart 
• A total of four haploid daughter cells will be produced, these are the gametes

The process of cell division by meiosis to produce haploid gamete cells

Comparing Mitosis & Meiosis Table