Cell division is the process where a single living cell
splits to become two or more distinct new cells. All cells
divide at some point in their lives. Cell division occurs in
single-celled organisms like bacteria, in which it is the
major form of reproduction (binary fission), or in
multicellular organisms like plants, animals, and fungi.
Many cells continually divide, such as the cells that line
the human digestive tract or the cells that make up human
skin. Other cells divide only once.
There are two major ways in which biologists categorize cell
division. The first, mitosis, is simple cell division that
creates two daughter cells that are genetically identical to
the original parent cell. The process varies slightly
between prokaryotic and eukaryotic organisms. In eularyotes,
mitosis begins with replication of the deoxyribonucleic acid
(DNA) within the cell to form two copies of each chromosome.
Once two copies are present, the cell splits to become two
new cells by cytokinesis, or formation of a fissure. Mitosis
occurs in most cells and is the major form of cell division.
The second process, called meiosis is the production of
daughter cells having half the amount of genetic material as
the original parent cell. Such daughter cells are said to be
haploid. Meiosis occurs in human sperm and egg production in
which four haploid sex cells are produced from a single
parent precursor cell. In both mitosis and meiosis of
nucleated cells, shuffling of chromosomes creates genetic
variation in the new daughter cells. These very important
shuffling processes are known as independent assortment and
random segregation of chromosomes.