Question
What is the difference between mitosis and meiosis? Draw a comparison and explain which type of cell division occurs where in the human body.
Solution — Step by Step
Mitosis is cell division for growth and repair — your body needs to replace old cells and grow new tissue. Meiosis is cell division for reproduction — it produces gametes (sperm and eggs) that carry half your genetic information.
The purpose dictates everything else about how each process works.
Mitosis has one division → 2 daughter cells. Meiosis has two divisions (Meiosis I + Meiosis II) → 4 daughter cells.
Why two divisions in meiosis? Because the whole point is to halve the chromosome number. One division separates homologous pairs; the second separates sister chromatids.
| Feature | Mitosis | Meiosis |
|---|---|---|
| Starting cell | Diploid (2n) | Diploid (2n) |
| Daughter cells | Diploid (2n) | Haploid (n) |
| Number of daughter cells | 2 | 4 |
| Genetic identity | Identical to parent | Genetically diverse |
| Crossing over | Does NOT occur | Occurs in Prophase I |
In humans, 2n = 46. So mitosis produces cells with 46 chromosomes; meiosis produces gametes with 23.
Mitosis occurs in somatic (body) cells — skin, liver, bone marrow, gut lining. Essentially everywhere except the gonads.
Meiosis occurs only in the gonads — testes (producing sperm) and ovaries (producing eggs). In females, meiosis is actually arrested at Prophase I until puberty, which is a fun fact examiners love.
Mitosis produces clones — genetically identical to the parent cell. This is what you want for replacing a dead skin cell.
Meiosis produces genetically diverse cells because of crossing over (exchange of segments between homologous chromosomes) and independent assortment. This genetic variation is the raw material for evolution.
Why This Works
The logic behind having two different division types comes down to ploidy maintenance. If gametes were produced by mitosis, each sperm and egg would have 46 chromosomes. At fertilisation, the zygote would have 92 — and the next generation would have 184. Meiosis prevents this chromosome doubling disaster by halving the count before fusion.
Crossing over in Meiosis I (specifically during Prophase I, when homologous chromosomes form bivalents) is not random chaos — it’s a controlled recombination that shuffles alleles between maternal and paternal chromosomes. This is why siblings from the same parents are not identical (unless they’re identical twins, who arise from a single fertilised egg splitting via mitosis).
For NEET, focus on the sequence: Interphase → Prophase I → Metaphase I → Anaphase I → Telophase I → Prophase II → Metaphase II → Anaphase II → Telophase II. Meiosis I is the reductive division; Meiosis II looks like mitosis but starts with haploid cells.
Alternative Method — The “Purpose Test”
When you’re confused in an exam about which division is happening, ask: what is the end product supposed to do?
- Body cell repair/growth → Mitosis (needs identical copies)
- Reproductive cells → Meiosis (needs half the chromosomes + genetic diversity)
This works even for organisms you’ve never studied. Yeast undergoing budding? Mitosis. Fern producing spores (which are haploid)? Meiosis. The purpose is always your first clue.
NEET PYQs frequently ask about the stages where chromosome number is reduced. The answer is always Anaphase I — when homologous chromosomes separate. At this point each pole gets n chromosomes (23 in humans). Anaphase II separates sister chromatids but doesn’t change the chromosome number further.
Common Mistake
Students write that meiosis produces “2 daughter cells” — confusing it with mitosis. Meiosis has two rounds of division, producing 4 haploid cells. In females, 3 of these 4 become polar bodies (non-functional) and only 1 becomes a mature egg — but the division still produces 4 cells initially. Don’t let the polar body situation confuse your count of how many cells meiosis produces.
Another trap: stating that crossing over occurs in mitosis. It does not. Crossing over is exclusive to Prophase I of meiosis. In mitosis, homologous chromosomes don’t even pair up — they line up individually at the metaphase plate.
Final Answer:
- Mitosis: 1 diploid cell → 2 identical diploid daughter cells. Occurs in somatic cells. No crossing over.
- Meiosis: 1 diploid cell → 4 genetically diverse haploid daughter cells. Occurs in gonads. Crossing over occurs in Prophase I.
The fundamental difference is purpose: mitosis is for growth and repair (needs copies), meiosis is for sexual reproduction (needs diversity and half the chromosome count).