Glossary
meiosis
Meiosis is the division that makes gametes: two divisions after one DNA replication turn one diploid cell into four haploid cells.
Meiosis is the division that produces gametes, and its result is the opposite of mitosis: four cells, each with half the chromosome number of the parent. It runs the cell cycle twice with only one round of DNA replication. In meiosis I, the reduction division, the homologous chromosomes find each other, line up as pairs, and are pulled apart, so each daughter cell receives one chromosome of each pair rather than both. In meiosis II the sister chromatids separate, exactly as they do in mitosis. In a human, 46 chromosomes go in and each of the four gametes carries 23, so that fertilization restores 46. The point of the two divisions is variety. Crossing over in prophase I exchanges segments between non-sister chromatids, and independent assortment at metaphase I decides at random which maternal and paternal chromosome travel together. That is why siblings from the same parents are genetically different, a question the exam likes to ask about mitosis by contrast.
Taught in
Related terms
- mitosis — Mitosis is the division that grows and repairs a body: one cell becomes two, and each daughter cell carries the same set of chromosomes as the parent.
- chromosome — A chromosome is one long DNA molecule wound around histone proteins, and a human body cell carries 46 of them, in 23 pairs.
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)