Overview of Cell Division

Cells reproduce through a process called cell division to create new daughter cells. Unicellular organisms like bacteria clone themselves, resulting in two genetically identical, separate organisms, a process known as binary fission or asexual reproduction.

In multicellular organisms, cell division produces new cells that are parts of the organism, essential for growth or replacing worn-out/injured cells. An example is skin cell division to heal a cut. A modified form of cell division also creates sex cells, known as gametes.

Chromosomes are crucial for cell division. Inside a cell's nucleus, the genetic material is DNA (deoxyribonucleic acid), which contains the genetic code for the organism. When spread out, DNA is called chromatin. Before division, DNA replicates itself and then condenses into X-shaped structures called chromosomes. Each side of the X is a genetically identical sister chromatid, joined in the middle by a centromere.

Different organisms have varying numbers of chromosomes. Human somatic cells (all body cells except gametes) have 23 pairs of chromosomes, totaling 46. Gametes (eggs and sperm) are an exception, possessing only one chromosome from each pair, totaling 23. Unlike somatic cells, gametes are not genetically identical to their parent cells. When a sperm fertilizes an egg, their 23 chromosomes combine to form a zygote with 23 pairs (46 total) of chromosomes.

This overview of cell division forms a basis for understanding the cell cycle, which is the complete life cycle of a cell.