Topic 17.2 · Supplement
Mitosis
The current Cambridge 0610 syllabus does not ask for the named stages of mitosis, which makes this page shorter than you might expect. What it does ask for is precise: what mitosis produces, why chromosome replication has to happen before division rather than after, and the specific list of processes that depend on it.
What mitosis produces
Mitosis is nuclear division that gives rise to genetically identical cells. The chromosome logic behind that result is: copy first, then separate the copies, then maintain chromosome number in each daughter cell.
Before mitosis happens, the chromosomes are replicated exactly — a complete copy of the genetic information is made. During mitosis, those chromosome copies separate, so that each daughter cell receives one full set. If the parent nucleus was diploid, both daughter nuclei remain diploid, because the copies are being split between the two daughters rather than each daughter keeping only half of the original information. It’s worth being careful with that last point in an answer: replication before mitosis is not a reason to say a daughter cell ends up with double the normal chromosome number — the copies are shared out, one full set per daughter.
The overall sequence, stated the way an examiner wants it: chromosomes replicate, the chromosome copies separate, and the daughter cells receive the same genetic information and the same chromosome number as the parent cell.
Why mitosis matters: its four roles
Cambridge names four processes that depend on mitosis, and all four rely on the same underlying property — that mitosis preserves genetic information exactly.
- Growth. A multicellular organism increases its number of cells by producing new, genetically identical cells.
- Repair of damaged tissues. Replacement cells for a damaged tissue are produced by mitosis.
- Replacement of cells. Cells that die or are lost during normal function are replaced by new cells produced by mitosis.
- Asexual reproduction. Producing genetically identical offspring from a single parent requires the offspring’s cells to be genetically identical to the parent’s — which is exactly what mitosis provides.
If an exam question asks why mitosis is important for one of these four processes specifically, the answer should name the process and connect it back to genetically identical cells, rather than describing mitosis in general terms.
Stem cells
Stem cells are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for particular functions. “Unspecialised” describes a cell that has not yet developed the particular structures a specialised cell needs for one specific role — it doesn’t mean the cell lacks genes or lacks a function of its own.
Mitosis is what supplies the new daughter cells in the first place; what happens after that, as covered on the protein synthesis and gene expression page, is that some of those daughter cells change which genes they express and develop into a specialised cell type. The genetic information stays essentially the same across specialised and unspecialised descendants of a stem cell — what changes is which parts of it are switched on.
Mitosis compared with meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Cells produced | genetically identical | genetically different |
| Chromosome number | maintained | halved |
| Ploidy | no change | diploid → haploid |
| Main role | growth, repair, replacement, asexual reproduction | production of gametes |
The two are easy to confuse if you only remember “division makes new cells” without the specific outcome each one produces. Mitosis preserves chromosome number and genetic information — it’s the division used whenever an organism needs more of the same kind of cell. Meiosis does the opposite on both counts, halving chromosome number and producing cells that are genetically different from one another, because it exists to make gametes for sexual reproduction rather than to make more body cells.