What's the difference between mitosis and meiosis?

Both are cell division and the stages sound identical (prophase, metaphase…). What's actually different between mitosis and meiosis, and why do we need both?

Mitosis is the photocopier: when you grow, heal a cut, or replace skin cells, your body needs exact copies — same 46 chromosomes, same genes. One division, two identical cells.

Meiosis is the deck-shuffler for reproduction. If egg and sperm each carried 46 chromosomes, a baby would have 92. So meiosis halves the count to 23 — and while it's at it, it shuffles the genetic deck, which is why siblings differ.

Mitosis: one division → 2 diploid (2n) daughter cells, genetically identical to the parent. Occurs in somatic cells for growth, repair and (in many organisms) asexual reproduction.

Meiosis: two successive divisions → 4 haploid (n) gametes, each genetically unique. Variation comes from crossing over between homologous chromosomes in prophase I and from the independent assortment of chromosome pairs at metaphase I.

Key structural difference: in meiosis I, homologous pairs line up together and separate (reducing 2n to n); mitosis never pairs homologues — it separates sister chromatids only.

Human skin cell dividing by mitosis: 46 chromosomes in, two cells with 46 identical chromosomes out. Human cells forming sperm by meiosis: 46 in, four cells with 23 out — and thanks to crossing over and assortment, each of those four carries a different combination of the parents' genes. Fertilisation restores 23 + 23 = 46.

• Saying meiosis is 'mitosis done twice' — the pairing and separation of homologous chromosomes in meiosis I has no counterpart in mitosis, and it's where the halving and most of the shuffling happen.
• Writing that mitosis produces 4 cells or meiosis 2 — swap-around errors are the most common exam slip; anchor it as mitosis: 1 division → 2 identical; meiosis: 2 divisions → 4 unique.

• NCERT Class 11 Biology, Ch. 10 — Cell Cycle and Cell Division
• Khan Academy — Mitosis and meiosis