Mitosis vs Meiosis: The Differences, Stage by Stage

Quick answer: Mitosis makes two genetically identical diploid cells from one parent cell, for growth and repair. Meiosis makes four genetically different haploid gametes from one parent cell, for sexual reproduction. Mitosis is a single division; meiosis is two divisions in a row. Chromosome number stays the same in mitosis and halves in meiosis.

I sit Cambridge IGCSE Biology, and this is where I lost the silliest marks of my year. A mock asked "Compare mitosis and meiosis" for four marks. I wrote four true things about meiosis - two divisions, four cells, crossing over, haploid - and got one mark. The examiner wanted four comparisons, in pairs, and I had written half of each one. Knowing the biology was never my problem. Writing it the way the mark scheme reads was.

Start with the job, not the stages

The fastest way to stop mixing these up is to remember what each division is for, because every other difference follows from that.

Mitosis makes more of the same cell. Skin replaces itself, a cut heals over, a root tip pushes into the soil. All of that needs exact copies, because a liver cell genetically different from its neighbours is a problem, not an upgrade. Uncontrolled mitosis is what a tumour is.

Meiosis makes gametes, produced only in the reproductive organs. Here copies would be a disaster: if a gamete carried the full 46 chromosomes, fertilisation would give 92, and the next generation 184. So meiosis halves the number and shuffles the genetic material on the way.

Follow the chromosomes: the count that fixes everything

Track chromosome number and chromatid number separately through both processes, because most lost marks come from treating them as the same thing. Start with a human cell: 46 chromosomes, arranged as 23 homologous pairs.

1. Interphase, G1. 46 chromosomes, 46 chromatids.
2. After DNA replication, S phase. Still 46 chromosomes, but now 92 chromatids - each chromosome is two identical sister chromatids joined at a centromere. This is the step people get wrong: copying the DNA does not change the chromosome number. A chromosome with two chromatids is still one chromosome.
3. Mitotic anaphase. Centromeres split and sister chromatids are pulled apart. Each pole receives 46 chromatids, which from that moment count as 46 chromosomes.
4. End of mitosis. Two cells, 46 chromosomes and 46 chromatids each, identical to the parent and to each other.

The same cell going through meiosis instead:

1. After replication. Identical start: 46 chromosomes, 92 chromatids.
2. Anaphase I. Whole homologous chromosomes are pulled apart, each still made of two chromatids. Each pole gets 23 chromosomes, which is 46 chromatids.
3. End of meiosis I. Two cells, 23 chromosomes and 46 chromatids each. The cell is already haploid, which is why meiosis I is the reduction division.
4. Meiosis II. No replication in between. Anaphase II splits sister chromatids, exactly as mitosis does.
5. End of meiosis II. Four cells, 23 chromosomes and 23 chromatids each.

Rebuild that ladder from memory and "how many chromatids are present at metaphase I" stops being frightening. The answer is 92.

Mitosis, stage by stage

Four stages, one division, and the wording examiners reward for each.

• Prophase. Chromosomes condense and become visible, each as two sister chromatids. The nuclear envelope breaks down and spindle fibres form.
• Metaphase. Chromosomes line up singly along the equator, attached to spindle fibres at their centromeres.
• Anaphase. Centromeres divide and spindle fibres shorten, pulling sister chromatids to opposite poles.
• Telophase. Chromosomes decondense and a new nuclear envelope forms around each set. Cytokinesis divides the cytoplasm.

PMAT is the order. If a question says describe rather than name, one accurate verb per stage - condense, line up, separate, reform - is where the mark sits.

Meiosis, stage by stage

Meiosis runs those four stages twice, but almost everything that matters happens the first time.

Meiosis I, the reduction division. In prophase I, homologous chromosomes pair up as bivalents and crossing over occurs. In metaphase I the bivalents line up as pairs - two rows on the equator, not one. In anaphase I the homologous chromosomes of each pair go to opposite poles, still as two-chromatid chromosomes. Telophase I gives two haploid cells.

Meiosis II, the equational division. Prophase II, metaphase II with chromosomes single file again, anaphase II where sister chromatids finally separate, then telophase II. Four haploid cells.

The exam-critical sentence: meiosis I separates homologous chromosomes, meiosis II separates sister chromatids. If you take one line from this article, take that one.

Where the variation actually comes from

Meiosis creates variation by three named mechanisms. Vague answers about "mixing the genes up" score nothing.

• Crossing over, in prophase I. Non-sister chromatids of a homologous pair break and rejoin at chiasmata, exchanging equivalent sections of DNA, so new combinations of alleles end up on the same chromosome.
• Independent assortment, in metaphase I. Each bivalent lines up with either member facing either pole, at random and independently of every other pair. With 23 pairs that alone gives 2^23 combinations, roughly 8.4 million.
• Random fertilisation. Any of those gametes can fuse with any gamete from the other parent.

Mitosis has none of these - no pairing, no crossing over, no random orientation - which is why its products are clones.

Answering a "compare" question properly

Comparison marks go to paired statements, never to facts about one process on its own. Not this: "Meiosis produces four cells." That is a fact. This: "Mitosis produces two daughter cells, whereas meiosis produces four."

Build your answer from these pairs, using the technical word every time - diploid, haploid, homologous, chromatid:

1. Mitosis involves one division, whereas meiosis involves two.
2. Mitosis produces two cells, whereas meiosis produces four.
3. Mitosis produces diploid cells, whereas meiosis produces haploid cells.
4. Mitosis produces cells genetically identical to the parent, whereas meiosis produces genetically different cells.
5. Crossing over and independent assortment occur in meiosis but not in mitosis.
6. Mitosis occurs in body cells for growth and repair, whereas meiosis occurs in the reproductive organs to form gametes.

Six pairs covers any four or six mark comparison on Cambridge IGCSE, GCSE with AQA, Edexcel or OCR, CBSE, AP Biology or WASSCE. Put each pair on /flashcards as one card, with the full "whereas" sentence as the answer.

Telling them apart in a diagram

Count the rows on the equator, then look at what is being pulled apart.

• Two rows of chromosomes on the equator means metaphase I. A single row means mitosis or metaphase II.
• Structures moving to the poles still joined at a centromere means anaphase I. Single chromatids means mitotic anaphase or anaphase II.
• Four cells in the final picture always means meiosis.

The errors I kept repeating: writing that meiosis "halves the DNA" instead of "halves the chromosome number", putting crossing over in metaphase I when it belongs in prophase I, and drawing a replication step between meiosis I and II. If a diagram keeps beating you, drop it into /explain and ask for it labelled stage by stage.

Test yourself

1. A cell with 12 chromosomes enters meiosis. How many chromosomes and how many chromatids are in each cell at the end of meiosis I?
2. Name the stage in which crossing over occurs, and the structures that exchange DNA.
3. Give two comparative statements, each using "whereas", that distinguish mitosis from meiosis.

Quick answers: (1) 6 chromosomes and 12 chromatids in each of the two cells. (2) Prophase I; non-sister chromatids of homologous chromosomes, at chiasmata. (3) For example, mitosis produces diploid cells whereas meiosis produces haploid cells.

Want these under exam conditions? Generate a set on /quiz, or work the wider topic on /help-in-study/biology.

FAQ

What is the main difference between mitosis and meiosis?

Mitosis is one division producing two genetically identical diploid cells for growth and repair. Meiosis is two divisions producing four genetically different haploid cells for sexual reproduction.

Does DNA replication happen before meiosis II?

No. DNA replicates once, in interphase before meiosis I, and never again between the two divisions. That is why the chromatid number halves during meiosis II while the chromosome number stays haploid.

Why is meiosis I called the reduction division?

Because the chromosome number is halved in meiosis I, when homologous pairs separate in anaphase I. By the end of telophase I each cell is already haploid, and meiosis II only separates sister chromatids.

Do plants carry out mitosis and meiosis too?

Yes. Root and shoot tips are the classic material for observing mitosis, and meiosis in plants produces the cells that form pollen and ovules. The stages are the same; the visible difference is cytokinesis, where a plant cell builds a cell plate instead of the membrane pinching inwards.

In short: mitosis copies, meiosis halves and shuffles. Track chromosome and chromatid numbers separately, remember that meiosis I separates homologues while meiosis II separates chromatids, and write every comparison as a paired "whereas" sentence - that is where the marks actually are.