Before mitosis, the cell creates an identical set of its own genetic information – this is called DNA replication. The genetic information is in the DNA of the chromosomes. At the beginning of mitosis the chromosomes wind up into visible objects that can be seen with a light microscope. The chromosomes are now two chromatids joined at the centromere. Since the two chromatids are identical to each other, they are called sister chromatids.
Mitosis happens in all types of dividing cells in the human body except with sperm and ova. The sperm and ova are gametes or sex cells. The gametes are produced by a different division method called meiosis.