There are two methods of cell division that are dependant on the type of cell: Mitosis and Meiosis. This system is meiosis and occurs in sex cells like sperm and ovums where the number of chromosomes needs to be halved.
Illustration of a generic eukaryotic cell undergoing the metaphase stage of meiosis I. Illustration of a cell during metaphase (I) of meiosis (gamete formation). During meiosis four daughter nuclei are formed from one parent nucleus after two stages of nuclear division. Meiosis occurs only in the sex cells (gametes) of the testes and ovaries. At metaphase (I) pairs of homologous chromosomes line up along the centre of the cell ready to be separated during anaphase (I). Separation results in two cells with half the usual number of chromosomes. The full complement is restored when two gametes fuse during fertilisation.