The cell cycle, mitosis and meiosis
DNA, in the form of chromosomes, is divided so that each daughter cell has a complete copy of the genetic material (or genome). Organisms that reproduce sexually have two copies of each chromosome, one from their father and one from their mother.
A special form of cell division needed to produce sex cells - for example, sperm and eggs with only one copy of each chromosome. Fusion of the sex cells creates a new individual with two copies of each chromosome.
Many single-celled organisms reproduce by cell division and have a single copy of each chromosome.