A form of cell division happening in sexually reproducing organisms by which two consecutive nuclear divisions (meiosis I and meiosis II) occur without the chromosomal replication in between, leading to the production of four haploid gametes (sex cells), each containing one of every pair of homologous chromosomes (that is, with the maternal and paternal chromosomes being distributed randomly between the cells)
Meiosis is a specialized form of cell division that ultimately gives rise to non-identical sex cells. There are two successive nuclear divisions: first meiotic division (or meiosis I) and second meiotic division (or meiosis II). Each of them has four major phases: prophase, metaphase, anaphase and telophase, and are also designated as I or II, depending on whether it occurs in meiosis I or meiosis II.
Before the cell enters meiosis, the chromosomes in a cell are duplicated (during the interphase). In meiosis I, the chromosomes condense along the center of the nucleus, and pair with their homologues during crossing over. Next, the pairs of chromosomes separate and move to opposite ends of the cell. The cell divides for the first time producing two cells. The two cells will undergo meiosis II wherein both of them divides further into two cells, each containing one of every decoupled chromosome’s sister strands (chromatids), thus, producing four genetically different, haploid cells.
Meiosis is a vital process because it reduces the original number of chromosomes to half, and allows genetic variability by genetic recombination and independent assortment. Meiosis produces four haploid cells that may develop into potential gametes so that when fertilization occurs, a new individual with the full number of genes results, thereby maintaining the integrity of chromosomal number across generations while promoting genetic diversity and variability in forms in the population.
Word origin: Greek meiōsis, meioun (to diminish), from meiōn (less)
- meiotic (adjective)