Mitosis vs Meiosis
Mitosis produces two genetically identical diploid daughter cells for growth and repair; Meiosis produces four genetically unique haploid cells for sexual reproduction.
Quick Comparison
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Production of sex cells (gametes) for sexual reproduction |
| Number of divisions | One division (PMAT) | Two divisions (Meiosis I and Meiosis II) |
| Daughter cells produced | 2 diploid cells (2n) | 4 haploid cells (n) |
| Genetic variation | Identical to parent cell (clones) | Genetically unique due to crossing over and independent assortment |
| Chromosome number | Maintained (diploid to diploid) | Halved (diploid to haploid) |
| Where it occurs | Somatic (body) cells throughout the organism | Only in germ cells (testes and ovaries) |
Key Differences
1. Number of Cell Divisions and Phases
Mitosis involves a single cell division with four main phases: Prophase, Metaphase, Anaphase, and Telophase (often remembered as PMAT), followed by cytokinesis. The process takes a few hours to complete and results in two daughter cells. The chromosomes replicate once during S phase of interphase, and the cell divides once.
Meiosis consists of two consecutive divisions: Meiosis I and Meiosis II. Each division has its own PMAT phases (Prophase I/II, Metaphase I/II, etc.). After one DNA replication event in S phase, the cell divides twice, creating four daughter cells. The entire process takes much longer — days to weeks depending on the organism and cell type.
2. Crossing Over and Genetic Recombination
Mitosis does not involve crossing over or genetic recombination. Sister chromatids separate during anaphase, but homologous chromosomes do not interact. The genetic material is replicated exactly and distributed identically to daughter cells, producing clones of the parent cell.
Meiosis includes crossing over (genetic recombination) during Prophase I, when homologous chromosome pairs (tetrads) exchange segments of DNA at points called chiasmata. This shuffling of genetic material between maternal and paternal chromosomes creates new combinations of alleles, ensuring each gamete is genetically unique and increasing genetic diversity in offspring.
3. Chromosome Number in Daughter Cells
Mitosis maintains the diploid chromosome number. A human somatic cell with 46 chromosomes (23 pairs) undergoes mitosis to produce two daughter cells, each with 46 chromosomes. The chromosome count remains 2n (diploid) across generations of cells. This is essential for maintaining genetic consistency throughout the body.
Meiosis reduces the chromosome number by half through a reductional division in Meiosis I, where homologous pairs separate. Human germ cells start with 46 chromosomes (2n) and produce gametes with 23 chromosomes (n, haploid). When gametes fuse during fertilization, the diploid number is restored in the zygote (23 + 23 = 46).
4. Biological Purpose and Function
Mitosis serves three primary purposes: growth (increasing cell number during development), tissue repair and regeneration (replacing damaged or dead cells), and asexual reproduction in some organisms. Your skin cells, liver cells, and blood cells all undergo mitosis. In humans, trillions of mitotic divisions occur daily to maintain tissues and organs.
Meiosis has one specialized function: producing haploid gametes (sperm and eggs in animals, pollen and ovules in plants) for sexual reproduction. This process is essential for sexual reproduction because it prevents chromosome doubling with each generation and introduces genetic variation that drives evolution and adaptation.
5. Genetic Variation in Offspring
Mitosis produces genetically identical daughter cells (barring rare mutations). Each daughter cell receives an exact copy of the parent cell's DNA. This is crucial for maintaining tissue integrity and proper organ function — you wouldn't want your liver cells suddenly having different genetic instructions than your other liver cells.
Meiosis generates maximum genetic diversity through two mechanisms: crossing over during Prophase I (recombination between homologous chromosomes) and independent assortment during Metaphase I (random alignment of chromosome pairs). These processes ensure that each gamete is genetically unique, so siblings from the same parents are different from one another.
When Each Occurs
Mitosis occurs during:
- Embryonic development (growing from one cell to trillions)
- Childhood and adolescent growth (increasing body size)
- Healing of wounds and tissue repair (skin, bone, muscle regeneration)
- Replacement of dead or damaged cells (red blood cells, intestinal lining)
- Asexual reproduction in single-celled organisms (bacteria, amoeba)
- Vegetative reproduction in plants (runners, tubers, budding)
Meiosis occurs during:
- Spermatogenesis in males (continuous production of sperm in testes)
- Oogenesis in females (egg cell maturation in ovaries)
- Pollen formation in flowering plants (anthers of flowers)
- Ovule development in plant reproduction (ovaries of flowers)
- Sexual reproduction preparation in all sexually reproducing organisms
- Anytime gametes (sex cells) need to be produced
Real-World Example
Mitosis: When you scrape your knee, skin cells at the wound edge undergo rapid mitosis to close the gap. Each skin cell divides to create two identical daughter cells with 46 chromosomes each. Over several days, millions of mitotic divisions replace the damaged tissue with new, genetically identical skin cells.
Meiosis: In human ovaries, a diploid germ cell (46 chromosomes) undergoes meiosis to produce one mature egg cell (23 chromosomes) and three polar bodies. During Meiosis I, maternal and paternal chromosomes exchange DNA segments through crossing over, ensuring the egg contains a unique combination of genetic information different from either parent.
Characteristics and Significance
Mitosis
Advantages
- Produces genetically identical cells for tissue consistency
- Fast and efficient (hours vs. days for meiosis)
- Enables rapid growth and tissue repair
- Maintains diploid chromosome number across cell generations
- Allows asexual reproduction (efficient for single organisms)
- No need for a mate to reproduce (in asexual species)
Limitations
- No genetic variation (all offspring are clones)
- Cannot reduce chromosome number for sexual reproduction
- Mutations are passed to all descendant cells
- No opportunity for genetic recombination
- Limited evolutionary adaptability in asexual species
Meiosis
Advantages
- Creates genetic diversity through crossing over and independent assortment
- Reduces chromosome number for sexual reproduction
- Enables evolution through new gene combinations
- Increases population adaptability to environmental changes
- Prevents chromosome doubling in each generation
- Combines beneficial traits from both parents
Limitations
- Slower and more complex than mitosis
- Requires specialized germ cells (not all cells can do this)
- Errors can lead to chromosomal abnormalities (Down syndrome, etc.)
- Requires two parents for reproduction (sexual reproduction)
- Energy-intensive process with multiple checkpoints