The Role of Meiosis (Edexcel GCSE Biology: Combined Science)

• Cells in reproductive organs divide by meiosis to form gametes (sex cells)
• The number of chromosomes must be halved when the gametes are formed
• Otherwise, there would be double the number of chromosomes after they join at fertilisation to form the zygote (fertilized egg)
• This halving occurs during meiosis, and so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different haploid gametes
• It 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
• We describe gametes as being haploid – having half the normal number of chromosomes
• Because of this double division, meiosis produces four haploid daughter cells

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

The importance of meiosis

• Produces gametes e.g. sperm cells and egg cells in animals or pollen grains and ovum cells in plants
• Increases genetic variation of offspring
• Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be genetically different from any others