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Cell Cycle, Mitosis, and Meiosis


The term meiosis (greek meiosis "diminution") refers to a special kind of cell division that leads to four genetically different daughter cells, each of which only contains half of the chromosomes of the mother cell. While mitosis produces the cells needed for growth and division of tissues in the body, meiosis forms gametes: either eggs or sperm. Meiosis involves two sequential cell divisions. Like mitosis, it is subdivided into six phases: prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.

Beyond this analogy, the first meiotic division (meiosis I) differs from normal mitosis in two important details:

  1. In metaphase, two rows of chromosomes are formed at the equatorial plate of the cell. This alignment of the homologous (corresponding) chromosomes from the father and mother is called synapsis.
  2. In the subsequent anaphase I, each pair of homologous chromosomes is separated while the two chromatids of each chromosome stay together.

After meiosis I, each of the daughter cells only contains a single set of chromosomes (1n) with two chromatids per chromosome (2c). Because the second meiotic division follows directly without an intervening interphase, the result is two more daughter cells with only one chromatid of a haploid chromosome (1n/1c). During the interphase that follows the single chromatids are replicated to form the typical gamete genome: 1n/2c.

Meiosis I and II
Schematic of Meiosis I

Note: Only the meta- and anaphases are examined in greater detail, in order to highlight the differences with mitosis.


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