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Mitosis is the process, in the cell cycle, by which the chromosomes in the cell nucleus are separated into two identical sets of chromosomes, each in its own nucleus. In general, mitosis is followed immediately by cytokinesis, which divides the cytoplasm, organelles, and cell membrane, and later karyokinesis, which divides the nucleus, dividing the cell into two new cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 20% of the cell cycle.

Mitosis occurs only in eukaryotic cells and the process varies in different groups. For example, animalsundergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while fungi such as Aspergillus nidulans and Saccharomyces cerevisiae (yeast) undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus. Prokaryoticcells, which lack a nucleus, divide by a process called binary fission.

The process of mitosis is fast and highly complex. The sequence of events is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are prophase, prometaphase , metaphase , anaphase, and telophase. During mitosis, the pairs of chromatids condense and attach to fibers that pull the sister chromatids to opposite sides of the cell. The cell then divides in cytokinesis , to produce two daughter cells.

Because cytokinesis often occurs in conjunction with mitosis, "mitosis" is often used interchangeably with "mitotic phase". However, there are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. The most notable occurrence of this is among the fungi and slime molds, but is found in various groups. Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of fruit fly embryonic development.Errors in mitosis can either kill a cell through apoptosis or cause mutations. Certain types of cancer can arise from such mutations.

Meiosis  is a special type of cell division necessary for sexual reproduction in eukaryotes, such as animals, plants and fungi. The number of sets of chromosomes in the cell undergoing meiosis is reduced to half the original number, typically from two sets (diploid) to one set (haploid). The cells produced by meiosis are either gametes(the usual case in animals) or otherwise usually spores from which gametes are ultimately produced (the case in land plants). In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm in males and egg cells or ova in females. Since meiosis has halved the number of sets of chromosomes, when two gametes fuse during fertilisation, the number of sets of chromosomes in the resulting zygote is restored to the original number.

Meiotic division occurs in two stages, meiosis I and meiosis II, dividing the cells once at each stage. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated, so that each chromosome has two sister chromatids , a diploid organism now has a tetraploid DNA amount in the cell. The first stage of meiosis begins with a cell that has (if it is from a diploid organism) two copies of each type of chromosome, one from each of the mother and father, called homologous chromosomes, each of which has two sister chromatids. The homologous chromosomes pair up and may exchange genetic material with each other in a process called crossing over. Each pair then separates as two cells are formed, each with one chromosome (two chromatids) from every homologous pair.

In the second stage, each chromosome splits into two; each half, each sister chromatid, is separated into two new cells, which are haploid. This occurs in both of the cells formed in meiosis I. Therefore from each original cell, four genetically distinct haploid cells are produced. These cells can mature into gametes.

Comparison chart

	Meiosis	Mitosis
Definition	A type of cellular reproduction in which the number of chromosomes are reduced by half through the separation of homologous chromosomes, producing two haploid cells.	A process of asexual reproduction in which the cell divides in two producing a replica, with an equal number of chromosomes in each resulting diploid cell.
Function	Genetic diversity through sexual reproduction.	Cellular reproduction and general growth and repair of the body.
Type of Reproduction	Sexual	Asexual
Occurs in	Humans, animals, plants, fungi.	All organisms.
Genetically	Different	Identical
Crossing Over	Yes, mixing of chromosomes can occur.	No, crossing over cannot occur.
Pairing of Homologs	Yes	No
Number of Divisions	2	1
Number of Daughter Cells produced	4 haploid cells	2 diploid cells
Chromosome Number	Reduced by half.	Remains the same.
Steps	(Meiosis 1) Prophase I, Metaphase I, Anaphase I, Telophase I; (Meiosis 2) Prophase II, Metaphase II, Anaphase II and Telophase II.	Prophase, Metaphase, Anaphase, Telophase.
Karyokinesis	Occurs in Interphase I.	Occurs in Interphase.
Cytokinesis	Occurs in Telophase I and in Telophase II.	Occurs in Telophase.
Centromeres Split	The centromeres do not separate during anaphase I, but during anaphase II.	The centromeres split during anaphase.
Creates	Sex cells only: female egg cells or male sperm cells.	Makes everything other than sex cells.