BiologyISC Class 11 · Cell Cycle and Cell Division

Meiosis: Prophase I Substages, Meiosis II and Differences from Mitosis

Updated 17 October 2026 · Fact-checked

Meiosis is a reductional division in which one diploid cell (2n) divides twice to form four haploid cells (n). Meiosis I separates homologous chromosomes and has a long prophase I with leptotene, zygotene, pachytene (crossing over), diplotene (chiasmata) and diakinesis; meiosis II separates the sister chromatids like mitosis.

Diagram of a red and a green homologous chromosome pair crossing over at a chiasma, then separating into two recombinant chromosomes. — Notice the chiasma, where the red and green homologous chromosomes swap segments, so the final chromosomes carry a mix of both.
Picture: Boumphreyfr · CC BY-SA 3.0 · Wikimedia Commons

Understand Meiosis: Stages and Significance

Where and why. Meiosis occurs in the formation of gametes (animals) or spores (plants) in sexually reproducing organisms. It reduces the chromosome number to half so that fertilisation restores the diploid number, and it creates genetic variation.

Meiosis I (reductional). *Prophase I:* *leptotene* (chromosomes condense and become visible); *zygotene* (homologous chromosomes pair up in synapsis, forming a bivalent or tetrad, joined by the synaptonemal complex); *pachytene* (bivalents are clearly visible as tetrads; crossing over between non-sister chromatids of homologous chromosomes, catalysed by recombinase, forming recombination nodules); *diplotene* (the synaptonemal complex dissolves and the homologues separate except at the X-shaped chiasmata, where crossing over occurred); *diakinesis* (terminalisation of chiasmata, nucleolus and nuclear envelope disappear, spindle assembles). *Metaphase I:* bivalents align at the equator, each homologue facing one pole. *Anaphase I:* homologous chromosomes (each with two chromatids) move to opposite poles; the centromeres do not split. *Telophase I:* two haploid cells form (with chromosomes still of two chromatids); nuclear envelopes may reappear. *Interkinesis:* a short gap with no DNA replication.

Meiosis II (equational). Prophase II, metaphase II, anaphase II (centromeres split and chromatids separate) and telophase II, followed by cytokinesis, forming four haploid daughter cells.

Significance. Keeps the chromosome number constant over generations; crossing over and independent assortment of chromosomes give genetic variation, the raw material for evolution.

Comparison. Mitosis: one division, two identical diploid cells, no pairing or crossing over, in somatic cells. Meiosis: two divisions, four haploid cells genetically different, with pairing and crossing over, in germ cells.

Meiosis: Stages and Significance: key facts

Prophase I: $L e pt o t e n e ∣ Z y g o t e n e ∣ P a c h y t e n e ∣ D i pl o t e n e ∣ D iak in es i s$; Synapsis, crossing over, chiasmata, terminalisation.
Result: 1.One 2n cell
2.two divisions
3.four n cells; Reductional division.
Chromosome counts (2n = 46): G2 46
After meiosis I 23
Anaphase II 46
Gametes 23; The number is halved at anaphase I.
Mitosis vs meiosis: $M i t os i s : 2 i d e n t i c a l 2 n ce l l s ∣ M e i os i s : 4 d i f f er e n t n ce l l s$; Equational versus reductional.

G2	46
After meiosis I	23
Anaphase II	46
Gametes	23

Meiosis: Stages and Significance in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Why siblings are not identical

Suppose two siblings born to the same parents look different from each other.

Explain two events in meiosis that account for this.

Try it first, then show the solutionSolution

Crossing over in pachytene exchanges segments between non-sister chromatids of homologous chromosomes, forming new combinations of alleles.
Independent assortment of the homologous pairs at metaphase I gives different combinations of maternal and paternal chromosomes in each gamete.
Random fusion of gametes adds further variation.

Answer: Crossing over and independent assortment give genetically different gametes.

Memory hook: Meiosis shuffles the genes; fertilisation shuffles again.

Tricks to remember Meiosis: Stages and Significance

Short memory aids. Say each one aloud once, then use it on a question the same day.

LZPDD
Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.
Use it when: Substages of prophase I.
Meiosis I reduces, meiosis II is like mitosis
Homologues separate in I; chromatids separate in II.
Use it when: Distinguishing the two divisions.

Meiosis: Stages and Significance: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Stage of crossing over · 1 mark · MCQBoard level

Crossing over takes place in the:
(a) leptotene
(b) zygotene
(c) pachytene
(d) diakinesis

Try it first, then show the solutionSolution

Crossing over between non-sister chromatids occurs in pachytene.

Answer: (c) pachytene

Example 2: Prophase I · 3 marks · Short answerBoard level

Name the substages of prophase I of meiosis and state what happens in zygotene and diplotene.

Try it first, then show the solutionSolution

Leptotene, zygotene, pachytene, diplotene and diakinesis. (1 mark)
Zygotene: homologous chromosomes pair (synapsis) forming bivalents with the synaptonemal complex. (1 mark)
Diplotene: the synaptonemal complex dissolves and homologues separate except at the chiasmata. (1 mark)

Answer: Five substages; synapsis in zygotene; chiasmata visible in diplotene.

Example 3: Chromosome number in meiosis · 4 marks · Short answerHarder board level

A cell has 2n = 12. Give the number of chromosomes and chromatids and the DNA content (C) at (i) G1, (ii) metaphase I, (iii) after telophase I, (iv) anaphase II and (v) in each gamete (2C in G1).

Try it first, then show the solutionSolution

G1: 12 chromosomes, 12 chromatids, 2C. (0.8 mark)
Metaphase I: 12 chromosomes (6 bivalents), 24 chromatids, 4C. (0.8 mark)
After telophase I: each cell has 6 chromosomes (24/2 = 12 chromatids), 2C. (0.8 mark)
Anaphase II: each cell has 12 chromosomes (single chromatids), 2C. (0.8 mark)
Each gamete: 6 chromosomes, 1C. (0.8 mark)

Answer: 12/12/2C; 12/24/4C; 6/12/2C; 12/12/2C (per cell); 6/6/1C.

Example 4: Mitosis and meiosis · 4 marks · Short answerHarder board level

Compare mitosis and meiosis in four points: where it occurs, number of divisions, daughter cells, genetic variation.

Try it first, then show the solutionSolution

Occurrence: somatic cells (mitosis); germ cells (meiosis). (1 mark)
Number of divisions: one (mitosis); two (meiosis). (1 mark)
Daughter cells: two diploid identical cells (mitosis); four haploid cells (meiosis). (1 mark)
Variation: none in mitosis; crossing over and independent assortment cause variation in meiosis. (1 mark)

Answer: Somatic versus germ cells; 1 versus 2 divisions; 2 versus 4 cells; no variation versus variation.

Example 5: Errors in meiosis · 5 marks · Long answerHOTS / competency

In a person, non-disjunction occurs in anaphase I so that one pair of homologous chromosomes goes to the same pole. (i) How many chromosomes will the four gametes have if 2n = 46? (ii) What will happen if such a gamete fuses with a normal gamete? (iii) Why is meiosis II "equational"?

Try it first, then show the solutionSolution

(i) Normal gametes have 23; with non-disjunction of one pair two gametes have 24 chromosomes and two have 22. (2 marks)
(ii) The zygote has 47 (trisomy) or 45 (monosomy) chromosomes, leading to a syndrome or non-viability. (1.5 marks)
(iii) Meiosis II separates sister chromatids so the number of chromosomes per cell remains the same, as in mitosis. (1.5 marks)

Answer: Two gametes with 24 and two with 22 chromosomes; trisomy or monosomy in zygotes.

Where students lose marks in Meiosis: Stages and Significance

The slips examiners see most often, and what to write instead.

Mistake: Putting crossing over in zygotene
Wrong substage.
Do this: Synapsis is in zygotene; crossing over in pachytene.
Usually costs: 1 mark.
Mistake: Writing that centromeres split in anaphase I
Confusing it with mitosis.
Do this: In anaphase I homologues separate and centromeres stay intact.
Usually costs: 1 to 2 marks.
Mistake: DNA replicating in interkinesis
Wrong statement.
Do this: There is no S phase between meiosis I and II.
Usually costs: 1 mark.

Exam tips

Draw the stages of prophase I in the correct order.
Make a table of chromosomes, chromatids and DNA for each stage.
State the term for each event: synapsis, crossing over, chiasma, terminalisation.
Mention the significance in terms of variation and constant chromosome number.

Practice questions on Meiosis: Stages and Significance

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The pairing of homologous chromosomes is called:
(a) synapsis
(b) cytokinesis
(c) terminalisation
(d) interkinesis
Hint
It occurs in zygotene.
Answer
(a) synapsis
Q2 · 2 marks · Short answerBoard level
What is a chiasma?
Hint
It is the X-shaped structure.
Answer
A chiasma is the X-shaped point of contact between non-sister chromatids of homologous chromosomes where crossing over occurred, seen in diplotene.
Q3 · 3 marks · Short answerHarder board level
Why is meiosis I called a reductional division?
Hint
Think of the chromosome number.
Answer
Homologous chromosomes separate, so the number of chromosomes per cell is halved from 2n to n.
Q4 · 3 marks · Short answerHarder board level
What is interkinesis? Is DNA replicated in it?
Hint
It is between the two divisions.
Answer
The short stage between meiosis I and meiosis II; DNA is not replicated, and the cell goes straight into prophase II.
Q5 · 3 marks · Assertion-reasonHarder board level
Assertion (A): Meiosis produces genetic variation. Reason (R): Crossing over and random orientation of bivalents at metaphase I recombine genes. Choose: (a) both true and R explains A (b) both true, R does not explain A (c) A true, R false (d) A false, R true.
Hint
Name the processes.
Answer
(a) Both are true and R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
Case study: Suppose a student examines a cell from the testis showing 23 bivalents at the equator.
(i) Identify the stage. (1 mark)
(ii) State the 2n number of the species. (1 mark)
(iii) State how many chromatids are present. (1 mark)
(iv) What will be the chromosome number in each cell after this division? (1 mark)
Hint
Each bivalent has two homologues, each with two chromatids.
Answer
(i) Metaphase I. (ii) 46. (iii) 92 chromatids. (iv) 23 chromosomes (each with two chromatids).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Substage of crossing over?Show answer
Pachytene.
2.Cells at the end of meiosis?Show answer
Four haploid cells.
3.Where do chiasmata appear?Show answer
Diplotene.
4.Division that separates homologues?Show answer
Meiosis I.

Meiosis: Stages and Significance: frequently asked questions

What is a bivalent?

A pair of synapsed homologous chromosomes, which with four chromatids is also called a tetrad.

Why is meiosis necessary for sexual reproduction?

Without it, the chromosome number would double in every generation when gametes fuse.

Does meiosis occur in bacteria?

No. Bacteria are haploid and divide by binary fission; meiosis occurs in eukaryotes.