Eukaryotic cells—those belonging to organisms more complex than bacteria and archaea—reproduce by copying their DNA and dividing into two new cells. Unlike the simple binary fission of prokaryotes, eukaryotic division occurs via two distinct processes: mitosis and meiosis.
Mitosis produces two genetically identical diploid daughter cells, each carrying the same 46 chromosomes as the parent. Meiosis, in contrast, consists of two successive divisions that generate four haploid cells with 23 chromosomes each. These haploid cells are genetically distinct from one another and from the parent.
Both processes start with a diploid parent cell that has duplicated its chromosomes into 92 chromatids. The key shared stages—prophase, metaphase, anaphase, and telophase—occur in each division, followed by cytokinesis.
In meiosis, these stages repeat in Meiosis I and Meiosis II. The unique genetic shuffling events—crossing over and independent assortment—occur during prophase I and metaphase I, respectively.
Mitosis is the universal mechanism for tissue growth, repair, and maintenance, occurring in virtually all somatic cells. Meiosis takes place exclusively in the gonads (testes and ovaries) and is responsible for producing gametes.
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Definition | Diploid parent cell divides into two identical diploid daughter cells. | Diploid parent cell undergoes two divisions to produce four haploid cells with increased genetic variation. |
| Function | Growth, repair, and maintenance of organism/cells. | Creation of cells for sexual reproduction. |
| Parent Cell Count | One | One |
| Division Events | One | Two (Meiosis I & II) |
| Chromosome Number (Parent) | Diploid (46) | Diploid (46) |
| Daughter Cells Produced | Two diploid cells | Four haploid cells (sperm or eggs) |
| Crossing Over | Does not occur | Occurs in prophase I |
| Reproduction Type | Asexual | Sexual |
| Key Steps | Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis | Interphase, Meiosis I (Prophase I–Telophase I), Meiosis II (Prophase II–Telophase II) |
| Homologous Pairs Present | No | Yes (in Meiosis I) |
| Location | All somatic cells | Only gonads |
Gametes—sperm in males and eggs in females—arise from meiosis. Human sperm carry either an X or Y chromosome; human eggs always carry an X chromosome. Each gamete is genetically half-identical to its parent but distinct from other gametes.
During prophase I, homologous chromosomes pair to form tetrads. Non-sister chromatids exchange DNA segments, creating new allele combinations while maintaining overall chromosome structure.
In metaphase I, tetrads align randomly along the metaphase plate. The orientation of each homologous pair is independent, generating a vast array of possible gamete combinations—2^23 ≈ 8.4 million in humans.
Somatic cells rely on mitosis to replace damaged or aged cells and to support growth. Turnover rates vary: brain cells divide rarely, whereas skin cells renew every few days. Stem cells in the bone marrow proliferate via mitosis to produce diverse blood lineages.
