Most cells have a limited lifespan. New cells are always required for growth, maintenance, and repair of an organism. Cell division is defined as the process in which a cell divides into two or more cells. Typically, about 10,000 trillion cell divisions occur over the lifetime of a human.
Mitosis is the term for a type of cell division that leads to the formation of two genetically identical cells, each of which is capable of dividing again. Somatic cells (cells forming the body of the organism and not involved in sexual reproduction) divide through mitosis.
In eukaryotes, another type of cell division, called meiosis, involves only germ cells (cells involved in sexual reproduction). Meiosis results in cells permanently transformed into gametes (a mature reproductive cell such as an egg or a sperm). Unlike mitosis, which maintains the original cell’s genome during multiple cycles of replication, meiosis reduces the number of chromosomes in a cell by half in the process of gamete formation. This ensures that when two gametes (one male and one female, each with half the genome of the organism) come together during sexual reproduction to form the zygote, the zygote’s genomic content is restored to that of the parent cells.
For this tutorial, we will consider cells from eukaryotic animals that are diploid (2n), meaning they carry two complete sets of homologous chromosomes.