When a human cell divides, its 46 chromosomes must be copied, or replicated, and each of the two new cells must receive exactly one copy of each chromosome. Mitosis (from the Greek mitos = thread) is the process that sorts the genetic material into two new nuclei and ensures that both contain exactly the same genetic information.

Embryos, babies and children grow using mitosis. It doesn't stop when they become adults. Mitosis occurs continuously in adults as new cells replace old ones such as worn-out blood cells or skin cells injured by cuts or burns.

Though mitosis is a smooth continuous process, biologists have divided it into several stages

Interphase
Interphase is the cell growth phase in which a cell increases in size and carries out activities that support the organism. It is technically not a part of mitosis. Near the end of this phase, the chromosomes of the cell duplicate in preparation for cell division. By the time a cell is ready to divide, there are two copies of each chromosome (the sister chromatids.)

The graphics below illustrate the stages of mitosis. Be sure to view the mitosis videos in the tabs above for review and more detail.

As interphase for the two new cells begins, the chromosomes uncoil and the cells begin to grow. . .

Mitosis chart Image courtesy of OpenStax [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons (modified for this website)

I thank the owners of the Cytographics website at
http://www.cytographics.com for permission to include the little clip at the top of the page showing mitosis in a living cell as seen through a microscope.