Cell division is the process that cells go through in order to divide. Cells may divide for several reasons, and there are two types of cell division depending on the purpose. The cell division associated with sexual reproduction is one type, called meiosis. The other type, the cell division associated with growth and cell replacement or repair, is called mitosis. In both types of cell division, the nucleus splits and DNA is replicated.
The cell division called mitosis produces daughter cells that have all the genetic material of the parent cell — a complete set of chromosomes. However, chromosomes are not the only material that needs to be divided and transferred to the daughter cells: there are cytoplasm and the cell membrane to divide as well. Cytokinesis is the process of dividing the cytoplasm and the cell membrane, and this process may follow immediately after mitosis or occur separately, depending on the organism involved. Together, these two processes make up the mitotic phases of the cell cycle.
The phases of cell division are prophase, metaphase, anaphase, and telophase, and these occur in both mitosis and meiosis. A fifth phases called prometaphase occurring between prophase and metaphase is designated by some, but not all sources. Interphase, which is not part of mitosis, is a preparatory stage during which the parent cell makes a copy of its genetic material so that each daughter cell can have a complete set. Therefore, mitosis is an ongoing and repetitive process, alternating with interphase.
Meiosis, on the other hand, reduces the number of chromosomes by half, so that, for example, human egg and sperm cells, called gametes, each have 23 chromosomes and can join to produce a zygote with 46. It has two division phases, whereas mitosis has only one. Meiosis in animals is called gametogenesis, specifically, spermatogenesis, producing sperm, in males and oogenesis, producing eggs or ova, in females. In the unfused state, the egg and sperm are called haploid cells — having only a single set of chromosomes, and they become diploid — having a pair of each type of chromosome — again when they unite during fertilization.
Meiosis specifically works to combine the genetic material of two individuals. When there is only one parent in the reproductive cycle — for example, in ferns, which reproduce through spore — the daughter cell must have the full genetic material — all the chromosomes — of the parent cell. Therefore, in the case of the creation of spore — sporogenesis — reproduction is accomplished without meiosis.
