Meiosis
The birth of sex cells: the source of genetic diversity
Summary
Meiosis is the special division that produces sex cells (sperm and eggs). After two successive divisions (Meiosis I + Meiosis II), 4 haploid cells are formed. Thanks to crossing over, every child is genetically unique.
In depth
Unlike the division of body cells, meiosis produces sex cells. Mitosis makes two identical cells from one; meiosis makes 4 cells from one through two successive divisions and halves the number of chromosomes (diploid → haploid). In prophase of Meiosis I, homologous pairs stick together (synapsis) and swap pieces through crossing over, the main source of genetic shuffling. In anaphase I the homologous pairs separate (the key difference from mitosis, where sister chromatids separate). Meiosis II separates the sister chromatids, much like mitosis. The result: 4 haploid cells, each with a different arrangement of chromosomes, which is why even siblings can be so different.
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