Meiosis is the process of cell division that produces gametes, or sex cells, with half the number of chromosomes as normal body cells. During meiosis, the parent cell's chromosomes are duplicated and then split into four gamete cells. This ensures that when fertilization occurs, the resulting zygote will have the full number of chromosomes. Without meiosis reducing the number of chromosomes in gametes, fertilization would result in far too many chromosomes in the zygote. Errors during meiosis where the gamete ends up with an extra chromosome can lead to genetic disorders like Down syndrome if that gamete is involved in fertilization.