Mitosis vs Meiosis: Every Difference That Gets Tested
AP Biology / first-year college · 12 flashcards · 7 quiz questions · updated 2026-08-19
Both divisions use the same four phases and the same spindle machinery, which is exactly why they are easy to confuse. The difference is what the cell is trying to achieve: mitosis makes copies, meiosis makes variety.
One sentence carries most of the marks: mitosis separates sister chromatids once, meiosis separates homologous chromosomes first and sister chromatids second.
The comparison in one table
| Mitosis | Meiosis | |
|---|---|---|
| Divisions | One | Two (meiosis I and II) |
| Daughter cells | 2 | 4 |
| Chromosome number | Diploid → diploid (2n → 2n) | Diploid → haploid (2n → n) |
| Genetically | Identical to the parent | All four differ |
| Crossing over | No | Yes, prophase I |
| Homologues pair up | No | Yes — synapsis forms tetrads |
| Purpose | Growth, repair, asexual reproduction | Producing gametes |
| Where in humans | Every body cell | Testes and ovaries only |
What separates when
This is the single most tested distinction, and it is worth being able to state without hesitating.
- •Mitosis, anaphase: sister chromatids are pulled apart. Chromosome number per cell stays the same.
- •Meiosis I, anaphase I: whole homologous chromosomes are pulled apart, sister chromatids stay joined. This is the reduction division — 2n becomes n here, not in meiosis II.
- •Meiosis II, anaphase II: sister chromatids finally separate, exactly like mitosis but in a haploid cell.
Where the variety comes from
- •Crossing over in prophase I: homologues synapse into a tetrad (bivalent) and exchange segments at chiasmata, producing recombinant chromatids.
- •Independent assortment in metaphase I: each homologous pair lines up independently, giving 2ⁿ combinations — 2²³ ≈ 8.4 million in humans before crossing over is even counted.
- •Random fertilisation multiplies the two above by the same number again for the other gamete.
Human numbers worth memorising
- •Somatic cell: 46 chromosomes (23 pairs), diploid.
- •After DNA replication in S phase: still 46 chromosomes, but each has 2 sister chromatids — 92 chromatids.
- •After meiosis I: 23 chromosomes per cell, each still with 2 chromatids.
- •After meiosis II: 23 chromosomes per gamete, one chromatid each.
- •Fertilisation restores 46.
When it goes wrong
Nondisjunction is the failure of chromosomes to separate — in anaphase I (homologues) or anaphase II (sister chromatids). The result is a gamete with an extra or missing chromosome, and after fertilisation, a trisomy or monosomy such as trisomy 21.
Common mistakes
- ✗Saying the chromosome number halves in meiosis II. It halves in meiosis I, when homologues separate.
- ✗Describing crossing over as happening between sister chromatids. It happens between non-sister chromatids of homologous chromosomes.
- ✗Counting chromosomes by counting chromatids. A chromosome with two sister chromatids is still one chromosome.
- ✗Claiming mitosis produces genetically identical cells 'because there is no crossing over' — the real reason is that sister chromatids are identical copies.
- ✗Forgetting that DNA replicates only once, before meiosis I, for both divisions.
Flashcards
Tap a card to reveal the answer.
How many daughter cells does meiosis produce?⌄
Four, each haploid and genetically distinct.
What separates in anaphase I?⌄
Homologous chromosomes — sister chromatids stay attached.
What separates in anaphase II?⌄
Sister chromatids, as in mitosis.
Which division is the reduction division?⌄
Meiosis I: the cell goes from diploid to haploid.
When does crossing over occur?⌄
Prophase I, between non-sister chromatids of a homologous pair at chiasmata.
What is a tetrad?⌄
Two homologous chromosomes paired in synapsis — four chromatids in total.
What is independent assortment?⌄
Homologous pairs orienting randomly at metaphase I, giving 2ⁿ possible gamete combinations.
How many chromosomes does a human gamete carry?⌄
23 — one from each homologous pair.
How many times does DNA replicate in meiosis?⌄
Once, in S phase before meiosis I.
Where does mitosis occur in humans?⌄
In every somatic cell that divides — growth, repair and replacement.
What is nondisjunction?⌄
Failure of chromosomes or chromatids to separate, producing gametes with the wrong chromosome number.
Are the daughter cells of mitosis genetically identical?⌄
Yes — they receive identical sister chromatids, barring mutation.
Practice quiz
Answer first, then open the explanation.
1. In which stage do homologous chromosomes separate?
- A. Anaphase of mitosis
- B. Anaphase I
- C. Anaphase II
- D. Telophase I
Show answer
B. Anaphase I
Anaphase I is the reduction division: homologues are pulled to opposite poles with their sister chromatids intact.2. A human cell entering meiosis has how many chromosomes?
- A. 23
- B. 46
- C. 92
- D. 46 pairs
Show answer
B. 46
46 chromosomes in 23 homologous pairs. After replication each has two chromatids, but the chromosome count is still 46.3. Crossing over occurs between:
- A. Sister chromatids of the same chromosome
- B. Non-sister chromatids of homologous chromosomes
- C. Any two chromosomes in the cell
- D. Chromosomes and the spindle
Show answer
B. Non-sister chromatids of homologous chromosomes
Synapsis brings homologues together; the exchange is between non-sister chromatids at chiasmata.4. Which process produces genetically identical daughter cells?
- A. Meiosis I
- B. Meiosis II
- C. Mitosis
- D. Both meiosis I and II
Show answer
C. Mitosis
Mitosis distributes identical sister chromatids, so both daughters match the parent cell.5. How many possible chromosome combinations arise from independent assortment alone in humans?
- A. 23
- B. 46
- C. 2²³
- D. 23²
Show answer
C. 2²³
Each of the 23 pairs orients independently, giving 2²³ ≈ 8.4 million combinations before crossing over.6. DNA replication occurs how many times during meiosis?
- A. Once, before meiosis I
- B. Once, between meiosis I and II
- C. Twice
- D. Not at all
Show answer
A. Once, before meiosis I
A single S phase precedes meiosis I; there is no replication between the two divisions.7. Nondisjunction in anaphase II produces:
- A. Four normal gametes
- B. Two gametes with the wrong chromosome number and two normal
- C. Four abnormal gametes
- D. No gametes at all
Show answer
B. Two gametes with the wrong chromosome number and two normal
Only the second division is affected, so two of the four products carry an extra or missing chromatid-derived chromosome.
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