Meiosis is the specialized cell division of the germline that halves the diploid chromosome set and thereby produces the gametes.
Ontological classification
- is an event in the germline
- is disjoint from mitosis, the ordinary nuclear division
- has part: reductional division and meiotic recombination
- is a precondition for the establishment of genomic imprinting
What meiosis accomplishes
It is not a mere division but a programme securing three things at once:
- Pairing of homologues. The two copies of each chromosome — one maternal, one paternal — find one another and are physically bound together.
- Recombination. The paired homologues exchange segments by crossing over. This generates genetic novelty and at the same time establishes the physical connection through which the pairs come under tension in the spindle.
- Ordered distribution. Because the homologues are paired, exactly one of each pair travels to each pole.
The result is a complete haploid set, not merely a numerically halved one. This distinction carries the whole burden in assessing artificial procedures: euploidy is a statement about composition, not about number.
Why it cannot be replaced
Procedures seeking to turn a body cell into a germ cell must accomplish the halving somehow. Two routes are open.
One returns the cells to the germline so that they undergo a genuine meiosis — that is the route of in vitro gametogenesis via stem cells; in mice it has been taken. The other forces the division in an enucleated oocyte cytoplasm without rebuilding the programme — that is mitomeiosis. There the pairing is missing, and without pairing each chromosome decides independently. Ordered distribution following an artificially forced reductional division has so far succeeded in no species.
Ageing
Female meiosis begins before birth, rests for decades, and is completed only at ovulation. Cohesion between chromosome pairs weakens over that time — the reason for the steeply rising aneuploidy rate of human oocytes with maternal age. Natural human meiosis is thus itself strikingly error-prone in distribution; “solved” would therefore not mean “error-free” for an artificial procedure, but “at the accustomed level.”
See also
- Germline, Gamete, Oocyte
- Genomic Imprinting
- Mitomeiosis, In Vitro Gametogenesis
- Somatic Cell Nuclear Transfer (SCNT)
- Fertilization
Sources: Generated by querying the Personhood ontology. Research as of 27 July 2026.