The Role of Meiosis (Edexcel GCSE Biology)

The Role of Meiosis

• 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