Mitosis is the phase when a cell is divided into two nuclei during the cell cycle. Even though the cells are supposed to divide, there are times when they do not. During nondisjunction at least a pair of chromosomes do not divided and so there are an odd number of chromosomes. The five main stages of mitosis are prophase, prometaphase, metaphase, anaphase and telophase.
Before these five stages take place, the mitosis process goes through the interphase where the cells begin and try to get ready for the next five stages. During nondisjunction in mitosis, this takes place during the G2 phase where the cell is about to divide. Then it enters into the interphase and metaphase without the cell dividing appropriately.