Meiosis

Reproductive cell division only occurs in the gonads (ovaries and testes). It is the process by which gametes are formed from a germ cell.
During reproductive cell division, diploid germ cells, containing two sets of chromosome pairs, must undergo mitosis, meiosis, and cellular differentiation before developing into mature gametes (ovum or sperm). The resulting gametes, or sex cells are haploid, meaning they contain only one set of 23 chromosomes, half the amount of somatic cells. The production of gametes is essential for the joining of two genomes during sexual reproduction.
Before reproductive cell division, a germ cell must follow the equivalent preparatory steps as a somatic cell, proceeding through the G1 and S phases of the cell cycle. However, germ cells do not pass through the G2 phase; instead they stop at the end of the S phase.
Unlike mitosis, which occurs in one single round, reproductive cell division occurs in two successive rounds: meiosis I and meiosis II.
MEIOSIS I
Meiosis I is sometimes referred to as reductional division, as the number of chromosomes in each cell is reduced from the diploid number of 46, to the haploid number of 23.
Prophase I
Prophase 1 - Stage I During early prophase I, chromatin fibers condense and shorten to form individual chromosomes.
Prophase 1 - Stage II During late prophase I, the mitotic spindle, composed of microtubules, extends from pericentriolar material at each pole to the center of the cell. The spindle microtubules attach to the kinetochore of each chromosome as the nuclear envelope breaks up and the nucleolus diminishes.
Prophase 1 - Stage III In contrast to mitosis, the chromosomes are arranged in homologous pairs. Each pair of chromosomes contain a maternal and paternal copy. These copies contain similar genes, arranged in the same location as one another.
Metaphase I
During metaphase I, homologous pairs of chromosomes line up along the metaphase plate.
Sections of DNA may be exchanged between the two chromosomes of each homologous pair through a process known as crossing-over, which generates genetic variation.
Anaphase I
During anaphase I, the microtubules attached to each kinetochore shorten and one complete chromosome from each homologous pair is pulled towards each pole of the cell.
Microtubules, extending from pole to pole and not attached to a kinetochore, start to lengthen, elongating the cell in preparation for cytokinesis and the cytoplasm of the cell begins to divide.
In contrast to mitosis, during meiosis I, the chromatids of each chromosome do not separate.
Telophase I
During telophase I, the nuclear envelope reforms.
Cytokinesis is completed, and the microtubules of the mitotic spindle break up.
The two haploid daughter cells each contain half the number of chromosomes as the original germ cell. In females, one of the daughter cells will form a polar body and degenerate.
MEIOSIS II
Daughter cells formed during meiosis I, which have not degenerated, now enter the second stage of meiosis (meiosis II).
The events of meiosis II are similar to mitosis.
Prophase II
The nuclear membrane breaks up and the mitotic spindle, formed of microtubules, extends from pericentriolar material at either pole to the center of the cell. The spindle microtubules attach to the kinetochore of each chromosome as the nuclear envelope breaks up and the nucleolus diminishes.
Metaphase II
Chromosomes, led by the mitotic spindle, line up along the metaphase plate along the midline of the cell.
Anaphase II
The centromere and kinetochore at the center of each chromosome split, allowing them to separate into individual sister chromatids.
The sister chromatids become distinct chromosomes and are pulled to opposite poles of the cell by the mitotic spindle microtubules still attached to the kinetochore.
Microtubules, extending from pole to pole and not attached to a kinetochore, lengthen, elongating the cell in preparation for cytokinesis, and the cytoplasm of the cell begins to divide.
Telophase II
The nuclear envelope reforms, the nucleolus reappears, and the chromosomes uncoil back into chromatin.
Once the cell has split in two, the microtubules of the mitotic spindle break up.
In females, one of the resultant daughter cells will degenerate into a polar body. At the end of meiosis, one diploid germ cell has been divided to form four gametes in males, whereas in females, only one functional gamete has been produced.

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