Meiosis
Meiosis is a specialized form of cell division that reduces the chromosome number by half, producing four genetically unique haploid daughter cells from a single diploid parent cell. It is essential for sexual reproduction, generating gametes (sperm and egg cells) in animals and spores in plants and fungi. Genetic diversity is introduced through two key events: crossing over during prophase I and independent assortment of homologous chromosomes.
Meiosis I vs Meiosis II
| Feature | Meiosis I | Meiosis II |
|---|---|---|
| Type of division | Reductional | Equational |
| Chromosomes separated | Homologous pairs | Sister chromatids |
| Crossing over | Yes (prophase I) | No |
| Daughter cells produced | 2 haploid cells | 4 haploid cells |
| DNA replication before | Yes | No |
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Related Terms
Mitosis
Mitosis is the process of nuclear division in eukaryotic cells that produces two genetically identical daughter nuclei, each containing the same chromosome number as the parent cell. It is the primary mechanism of growth, tissue repair, and asexual reproduction in multicellular organisms. Mitosis proceeds through four sequential stages — prophase, metaphase, anaphase, and telophase — before the cytoplasm divides in cytokinesis.
Prophase
Prophase is the first and typically longest stage of mitosis, during which chromatin condenses into distinct, visible chromosomes and the mitotic spindle begins to assemble. The nuclear envelope breaks down toward the end of prophase, and each chromosome is revealed as two sister chromatids joined at the centromere. In meiosis, prophase I is particularly significant because homologous chromosomes pair up (synapsis) and exchange genetic material through crossing over.
Cytokinesis
Cytokinesis is the physical process of cytoplasmic division that follows telophase and separates the two daughter nuclei into two distinct cells. In animal cells, a contractile ring of actin and myosin filaments forms a cleavage furrow that pinches inward until the cell splits. In plant cells, a cell plate grows outward from the center of the cell toward the plasma membrane, eventually forming a new cell wall between the two daughter cells.
From Greek "meioun" meaning to lessen or diminish, reflecting the halving of chromosome number; the term was introduced by J.B. Farmer and J.E.S. Moore in 1905.