What is meiosis and why is it important in inheritance?

Meiosis is a type of cell division that reduces the chromosome number by half, resulting in four genetically distinct haploid cells. This process is crucial for sexual reproduction and genetic diversity, as it ensures that offspring inherit a unique combination of genes from both parents, which is a fundamental aspect of inheritance studied in Cambridge IGCSE Biology.

How does meiosis differ from mitosis in terms of process and outcome?

Meiosis consists of two consecutive divisions, meiosis I and meiosis II, leading to four non-identical haploid cells, whereas mitosis results in two identical diploid cells. Meiosis introduces genetic variation through processes like crossing over and independent assortment, which are not present in mitosis. Understanding these differences is key in the Cambridge IGCSE Biology curriculum.

What are the stages of meiosis and what occurs in each stage?

Meiosis includes two main stages: meiosis I and meiosis II. Meiosis I involves homologous chromosomes pairing and exchanging genetic material during prophase I, aligning at the metaphase plate in metaphase I, separating during anaphase I, and finally forming two cells in telophase I. Meiosis II resembles mitosis, where sister chromatids separate, resulting in four genetically unique haploid cells. These stages are essential for understanding genetic variation in inheritance.

How does crossing over during meiosis contribute to genetic variation?

Crossing over occurs during prophase I of meiosis when homologous chromosomes exchange segments of genetic material. This process creates new combinations of alleles on each chromosome, contributing to genetic diversity among offspring. This genetic variation is a key concept in the study of inheritance in Cambridge IGCSE Biology.

Why is meiosis essential for sexual reproduction in organisms?

Meiosis is essential for sexual reproduction because it produces gametes (sperm and eggs) with half the number of chromosomes, ensuring that when fertilization occurs, the resulting zygote has the correct diploid number. This process maintains chromosome number across generations and introduces genetic diversity, which is a fundamental principle in the study of inheritance in Cambridge IGCSE Biology.

Why is "Saying meiosis produces 2 daughter cells." a common mistake in Meiosis?

Why it happens: Mitosis does. How to avoid it: Meiosis = TWO division stages → produces FOUR daughter cells. (Mitosis = ONE division stage → 2 daughter cells.)

Why is "Saying meiosis happens everywhere." a common mistake in Meiosis?

Why it happens: All cells divide. How to avoid it: Meiosis only happens in REPRODUCTIVE TISSUES (ovaries, testes; in plants in flowers). Body cells do mitosis only.

InheritanceCambridge IGCSE Biology (0610)

Meiosis

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Meiosis — Cambridge IGCSE 0610 Biology Extended (2026)

Cell division to make GAMETES. Halves the chromosome number. Introduces variation between offspring.

What you’ll learn

Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).

17.4 — Define meiosis.
17.4 — State outcome (4 haploid different daughter cells).
17.4 — Explain how meiosis produces variation.
17.4 — Compare mitosis and meiosis.

What is meiosis?

1 diploid cell → 4 haploid genetically different daughter cells. Used to make gametes.

Definition. Meiosis = nuclear division producing FOUR genetically DIFFERENT daughter cells, each with HALF the chromosome number of the parent cell.

Why halve the chromosome number?

Gametes will FUSE at fertilisation.
If gametes were diploid (46), zygote would be 92 — chromosome doubling each generation.
By halving in meiosis, fertilisation restores the diploid count.

Where it happens.

ANIMALS: in OVARIES (making eggs) and TESTES (making sperm).
PLANTS: in flowers (making pollen and ovules).
Restricted to reproductive tissues only.

The two stages.

Meiosis I: chromosomes pair up; DOUBLED CELL DIVIDES into 2 (each cell still with full chromosome number, but each chromosome has 2 sister chromatids).
Meiosis II: each cell divides AGAIN; sister chromatids separated → 4 cells.
Result: 4 cells, each haploid, each genetically different.

(IGCSE doesn't go into the prophase/metaphase detail. Just know the outcome.)

Worked qualitative. A human cell with 46 chromosomes goes through meiosis. How many chromosomes do the resulting gametes have?

46 → halved → 23 each.
Four gametes, each with 23 chromosomes.

Cambridge tip. Always state '4 different daughter cells' AND 'half chromosome number'. Both are key.

Diploid → haploid.
1 → 4 daughter cells.
Daughters genetically different.
Only in reproductive tissues.

How meiosis produces variation

Random assortment + crossing over → each gamete unique.

Two main mechanisms create genetic variation between gametes:

1. Random assortment.

Each chromosome pair lines up randomly.
Whether the maternal or paternal chromosome of each pair goes to which daughter cell is RANDOM.
With 23 chromosome pairs, that's 2²³ = 8 million different combinations.
Each gamete gets a unique random mix.

2. Crossing over.

Before they separate, paired chromosomes can EXCHANGE pieces with each other.
Maternal and paternal segments swap.
Creates new combinations of alleles on each chromosome.
Multiplies the variation enormously.

3. Random fertilisation.

Once gametes are formed, ANY sperm can fertilise ANY egg.
Adds another layer of randomness.

Total variation. Between random assortment + crossing over + random fertilisation, the genetic combinations possible from two parents are essentially infinite. That's why siblings (except identical twins) are never identical.

Worked qualitative. Why are identical twins genetically identical?

One sperm fertilises one egg → one zygote (with one specific genetic combo).
Zygote SPLITS into two embryos very early in development.
Both embryos have the same genome.
Fraternal twins: TWO eggs fertilised by TWO sperm → completely separate genetic combos (just like normal siblings born at the same time).

Cambridge tip. When asked HOW meiosis produces variation, give random assortment + crossing over. Saying 'because gametes are different' is circular.

Random assortment of pairs.
Crossing over (chunk swap).
Random fertilisation.
Sibling uniqueness (except identical twins).

Mitosis vs meiosis

Mitosis = same. Meiosis = halved. Different roles.

Feature	Mitosis	Meiosis
Daughter cells	2	4
Chromosome number	Same as parent	Halved
Diploid → ?	Diploid	Haploid
Genetic identity	Identical clones	All different
Where	All body cells (most tissues)	Reproductive tissues only
Purpose	Growth, repair, asexual	Make gametes for sexual reproduction
Variation	None	Yes (assortment + crossing over)

Worked qualitative. Could a body cell suddenly do meiosis instead of mitosis?

No — meiosis requires specific cellular machinery activated only in gonads.
Body cells do not undergo meiosis.
A skin cell stays diploid and clones itself — never reduces chromosome number.

Cambridge tip. Cambridge often gives a 'compare and contrast' table. Memorise it row by row.

Mitosis: 2 identical daughters. Meiosis: 4 different.
Mitosis: same chromosome number. Meiosis: halved.
Mitosis: growth/repair. Meiosis: gametes.
Different cellular machinery; different tissues.

How it’s examined

Meiosis appears Paper 4 (5-7 marks: define, contrast with mitosis, explain variation). Examiner reports flag students saying meiosis makes 2 daughters and missing the 'genetically different' point.

Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (17.4); 0610/42 Oct/Nov 2024 — Q18 (meiosis); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Meiosis

Step-by-step solutions to past-paper-style questions on meiosis, written exactly the way a tutor would explain them at the board.

1Define meiosis
Core• definition
Question
Define MEIOSIS and state the outcome.
Step-by-step solution
1. Step 1
  Meiosis = nuclear division producing FOUR genetically DIFFERENT daughter cells, each with HALF the chromosome number of the parent cell.
2. Step 2
  Diploid (2n) → haploid (n).
3. Step 3
  Used to make GAMETES (sperm + egg in animals; pollen + ovule in plants).
Answer
Meiosis: diploid cell → 4 different haploid daughters. Used for gamete production.
2Mitosis vs meiosis
Extended• Adapted from 0610/42 Oct/Nov 2024 Q18• comparison
Question
Compare MITOSIS and MEIOSIS.
Step-by-step solution
1. Step 1
  Mitosis: 1 → 2 daughter cells. Same chromosome number. Genetically identical. Used for growth, repair, asexual reproduction.
2. Step 2
  Meiosis: 1 → 4 daughter cells. Halved chromosome number. Genetically DIFFERENT. Used for gametes only.
Answer
Mitosis: 2 same-chromosome-number identical daughters (growth/repair). Meiosis: 4 half-chromosome-number different daughters (gametes).
3Why meiosis produces VARIATION
Extended• variation
Question
Explain TWO ways meiosis introduces VARIATION between gametes.
Step-by-step solution
1. Step 1
  Random assortment: when chromosomes line up to be separated, which one goes to which daughter cell is RANDOM. Each gamete gets a random mix of paternal and maternal chromosomes.
2. Step 2
  Crossing over: chromosomes can EXCHANGE pieces with their partner during meiosis → new combinations of alleles on the same chromosome.
3. Step 3
  Plus: random which sperm fertilises which egg, multiplying the variation further.
Answer
Random assortment of chromosomes + crossing over (exchanging pieces) → each gamete genetically unique.

Key Definitions and Keywords — Meiosis

Definitions to memorise and the exact keywords mark schemes credit for meiosis answers — sharpened from recent examiner reports for the 2026 0610 sitting.

Meiosis
Examiner keyword
Nuclear division producing 4 genetically DIFFERENT daughter cells, each with HALF the chromosome number of the parent. Produces gametes.
Haploid
Having ONE set of chromosomes (e.g. n=23 in humans). Result of meiosis. Gametes are haploid.

Common Mistakes and Misconceptions — Meiosis

The traps other students keep falling into on meiosis questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.

✕Saying meiosis produces 2 daughter cells.
Why it happens
Mitosis does.
How to avoid it
Meiosis = TWO division stages → produces FOUR daughter cells. (Mitosis = ONE division stage → 2 daughter cells.)
✕Saying meiosis happens everywhere.
Why it happens
All cells divide.
How to avoid it
Meiosis only happens in REPRODUCTIVE TISSUES (ovaries, testes; in plants in flowers). Body cells do mitosis only.

Practice questions

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Meiosis — frequently asked questions

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Meiosis

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Define meiosis

2Mitosis vs meiosis

3Why meiosis produces VARIATION

Meiosis

Haploid

✕Saying meiosis produces 2 daughter cells.

✕Saying meiosis happens everywhere.

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Meiosis — frequently asked questions