Revision for gcse additional science.
Meiosis is used in the body to make gametes, or sex cells such as ova and sperm in humans. These gametes are haploid. This means they have half the normal number of chromosomes. Humans have 46 chromosomes in total, arranged into 23 pairs. Gametes have only 23 chromosomes in total. This is because during sexual reproduction when the sperm and ova join together they both bring 23 chromosomes which join together to form the original 46 in the zygote. If there were 46 chromosomes in each gamete every generation would have double the amount of chromosomes of the previous generation, and soon the nucleus would be too big to fit into the cell. If there are too many or too few chromosomes in the nucleus the cell either dies, or the child is born with a condition such as downs syndrome.
Meiosis is used to produce these cells because meiosis results in haploid cells. It only occurs in the reproductive organs of an organism. Unlike mitosis, meiosis produces 4 cells which are non identical.
Before the cell begins to divide each chromosome in the cell replicates, and the chromosomes are pulled to the centre of nucleus and form pairs with another pair of chromosomes. 1 pair form each set of 2 chromosomes is pulled to one side, the other pair goes to the other side of the cell, and each side forms a new nucleus.
In each nucleus the cells are lined up at the centre and pulled apart by cell fibres, and these 2 nuclei split to form 4 non identical haploid cells.