When two gametes unite at fertilisation, the resulting cell has a combination of genes that is different from either parent. Each cell has two sets of chromosomes; one from the male parent and one from the female parent. Therefore the chromosomes exist in homologous pairs. During the first meiotic division, the homologous pairs of chromosomes separate. When they separate, they do so at random. Each member of the pair moves to opposite poles. The way one pair of chromosomes separate is unaffected by the way any of the other pairs separate. This random assortment take place for each of the 23 pairs of human chromosomes. The total number of combinations is 2²³. This assortment occurs for the eggs and the sperm cells. When a sperm fertilises an egg, the resulting fertilised cell contain a combination of genes arranged in an order that has most likely never occurred before and will probably never occur again