Think about what happens when a sperm meets an egg. Each one carries half the number of chromosomes of a normal body cell. When they fuse, the full number is restored. If sperm and egg were made by ordinary cell division (mitosis), each would have the full set — and fusion would double it every generation. That would be a disaster.
So nature invented a special division that cuts the chromosome number in half. That is meiosis.
The core idea in one sentence
Meiosis is a two-step division process that converts one diploid cell (2n) into four haploid cells (n), each genetically different from the parent and from each other.
The "two-step" part is crucial. Unlike mitosis, which is a single division, meiosis happens in two consecutive rounds: Meiosis I and Meiosis II.
Why two rounds?
The first round, Meiosis I, is the reductional division. Here, homologous chromosomes (one from each parent) pair up and then separate. The chromosome number drops from diploid to haploid. Each daughter cell after Meiosis I has one copy of each chromosome — but each chromosome still consists of two sister chromatids.
The second round, Meiosis II, is the equational division. It looks very much like mitosis. The sister chromatids finally separate. Each of the two cells from Meiosis I divides again, giving four haploid cells in total.
Note
The key difference between the two rounds: in Meiosis I, homologous chromosomes separate; in Meiosis II, sister chromatids separate.
What happens to the chromosomes?
Start with a diploid cell. For a human, that means 46 chromosomes — 23 pairs. Each pair consists of one chromosome from your mother and one from your father. These are homologous chromosomes.
Before meiosis begins, DNA replication happens once, just like before mitosis. So each chromosome now has two identical sister chromatids. But the chromosome number is still 46 (each chromosome, even with two chromatids, counts as one chromosome).
Meiosis I — the homologous pairs line up together, exchange segments (crossing over), and then get pulled to opposite poles. The cell divides. Now you have two cells, each with 23 chromosomes. But each of those 23 chromosomes still has two chromatids. The number has been halved: from 46 to 23.
Meiosis II — no further DNA replication. The chromosomes line up again, and this time the sister chromatids separate. Each of the two cells divides, giving four cells. Each has 23 chromosomes, and each chromosome is now a single chromatid.
2nMeiosis I2 cells (n, each chromosome with 2 chromatids)Meiosis II4 cells (n, each chromosome with 1 chromatid)
Why does this matter for exams?
Two things make meiosis different from mitosis, and both happen in Meiosis I:
Reduction of chromosome number — from 2n to n.
Genetic recombination — crossing over between homologous chromosomes shuffles the genetic material.
The result is four genetically unique haploid cells. In males, all four become sperm. In females, only one becomes a functional egg; the other three become polar bodies that degenerate.
The precise statement
Meiosis is a specialised type of cell division that reduces the chromosome number by half through two successive divisions: a reductional division (Meiosis I) in which homologous chromosomes separate, followed by an equational division (Meiosis II) in which sister chromatids separate, producing four genetically distinct haploid daughter cells from one diploid parent cell.
This concept is part of the Cell Cycle and Cell Division chapter in the CBSE Class 11 Biology syllabus and is frequently tested in NEET and state-level medical entrance exams. Many learners search "Meiosis Overview notes class 11" or "Meiosis Overview explained with diagram" while preparing for this unit.
Meiosis is the division that produces gametes, and gametes only have a role in sexual reproduction, where two of them fuse at fertilisation to form a new individual.
Meiosis is encountered during gametogenesis, the formation of gametes, in both plants and animals.
It reduces the chromosome number to the haploid level precisely so that, when two gametes fuse, the original diploid number is restored rather than doubled.
Vegetative reproduction, by contrast, produces new individuals from ordinary body cells without forming gametes at all, so it has no need for a chromosome-halving division.
✓Final answer
The correct choice is (A) Sexual reproduction — meiosis occurs specifically to form the gametes that sexual reproduction depends on.
Meiosis is tied to sexual reproduction because its entire purpose is to produce the haploid gametes that fuse at fertilisation.
Sexual reproduction depends on the fusion of two gametes, each carrying a complete haploid set of chromosomes. Gametes are not produced directly by ordinary cell division; instead, specialised diploid cells set aside for this purpose undergo meiosis, a division that halves the chromosome number and yields haploid daughter cells. This is why meiosis is specifically described as being encountered during gametogenesis, the formation of gametes, in both plants and animals.
Vegetative reproduction works on an entirely different principle. New individuals arise from ordinary somatic parts of the parent — stems, roots, buds and similar structures — without the formation or fusion of gametes at all. Because no gamete is being made, there is no need for a chromosome-halving division; ordinary equational (mitotic) division, which keeps the chromosome number unchanged, is what maintains these tissues and allows them to regenerate a whole new plant.
Note
The reason meiosis is essential specifically for sexual reproduction is the arithmetic of fertilisation: if gametes were diploid, fusing two of them would double the chromosome number every generation. Halving it first in meiosis, then restoring it at fertilisation, is what keeps a species' chromosome number constant across generations.
✓Final answer
In short, meiosis occurs during (A) Sexual reproduction, since it is the process that specifically produces the haploid gametes sexual reproduction requires.
Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.
CBSE 2026Set ANNUAL1 markMCQ
Q.The phase between Meiosis I and Meiosis II is
(a) Prophase II
(b) Interkinesis
(c) Karyokinesis
(d) Diplotene
›Reveal solutionSolution
Interkinesis is the short interval, without DNA replication, that separates the two meiotic divisions.
Meiosis involves two successive divisions: Meiosis I (reductional division, halving chromosome number) followed by Meiosis II (equational division, similar to mitosis). Between the end of telophase I and the start of prophase II, cells pass through a brief phase called interkinesis, which is usually short-lived and, critically, does NOT involve replication of DNA (since the chromosome number is already reduced and each chromosome already has two sister chromatids from the pre-meiotic S-phase).
Prophase II (a) is the first stage of the second meiotic division, occurring AFTER interkinesis, not the interval itself. Karyokinesis (c) is the general term for nuclear division (applicable to any division phase, not specifically this gap). Diplotene (d) is a sub-stage within prophase of Meiosis I itself, not the phase between Meiosis I and II.
✓Final answer
(b) Interkinesis.
CBSE 2026Set ANNUAL1 mark
Q.What are Meiocytes?
›Reveal solutionSolution
Meiocytes are diploid cells specialised to undergo meiosis, halving the chromosome number to produce haploid products.
In a sexually reproducing organism, not all cells divide by meiosis — only certain designated diploid cells, called meiocytes, are competent to undergo meiosis. During meiosis, a single meiocyte undergoes one round of DNA replication followed by two successive nuclear divisions (meiosis I and meiosis II), producing four haploid (n) daughter cells. In animals, meiocytes give rise to gametes (sperm/egg); in flowering plants, they give rise to spores — for example, pollen mother cells (microsporocytes) undergo meiosis to form the four microspores of a pollen tetrad, and megaspore mother cells similarly produce megaspores.
✓Final answer
Meiocytes are the diploid cells that undergo meiosis to produce four haploid cells (gametes/spores).
CBSE 2023Set ANNUAL1 mark
Q.Fill in the blank: ____ haploid cells are formed during meiotic division.
›Reveal solutionSolution
Meiosis produces four haploid daughter cells from one diploid parent cell.
Meiosis involves a single round of DNA replication followed by two successive divisions:
Meiosis I is the reductional division: homologous chromosomes pair (synapsis), exchange segments (crossing over) and then separate, halving the chromosome number from diploid (2n) to haploid (n) and giving two cells.
Meiosis II is like mitosis: the sister chromatids of each of those two cells separate, producing a total of four cells.
Because each of these final cells has half the parental chromosome number, all four are haploid, and (owing to crossing over and independent assortment) genetically distinct. This is why the correct fill for the blank is the number four.
✓Final answer
Four (4) haploid cells are formed during meiotic division.
CBSE 2022Set TERM11 markMCQ
Q.A type of cell division which reduces chromosome number to half is
(a) Mitosis
(b) Meiosis
(c) Both
(1) and
(2)
(d) None of these
›Reveal solutionSolution
Only meiosis reduces the chromosome number to half; mitosis maintains it.
Mitosis is an equational division: one diploid (2n) parent cell produces two diploid (2n) daughter cells with the SAME chromosome number as the parent -- used for growth and repair. Meiosis, in contrast, is a reductional division involving two successive divisions (meiosis I and meiosis II) but only ONE round of DNA replication: a diploid (2n) parent cell ultimately produces four haploid (n) daughter cells, each with HALF the chromosome number of the parent. This halving happens specifically at anaphase I, when homologous chromosomes (not sister chromatids) separate. Meiosis is essential in sexually reproducing organisms to produce gametes, so that fertilisation (fusion of two gametes) restores the diploid number in the offspring.
✓Final answer
(b) Meiosis.
CBSE 2022Set ANNUAL1 mark
Q.What type of cell division takes place in germ cells?
›Reveal solutionSolution
Meiosis is the type of division that occurs in germ cells to produce gametes.
Somatic (body) cells divide by mitosis, producing two genetically identical diploid daughter cells for growth and repair. Germ cells (in the gonads — testes and ovaries), however, undergo meiosis, a special two-step division (meiosis I and meiosis II) that reduces the chromosome number by half, from diploid (2n) to haploid (n), and also introduces genetic variation through crossing over and independent assortment. This ensures that when a haploid sperm fertilises a haploid egg, the resulting zygote returns to the normal diploid chromosome number of the species.
✓Final answer
Meiosis.
CBSE 2022Set ANNUAL1 markMCQ
Q.Which one is diploid structure?
(a) ovaries
(b) endosperm
(c) zygote
(d) All of these
›Reveal solutionSolution
Zygote is diploid (2n); endosperm is triploid → (c).
The zygote forms by fusion of two haploid gametes → it is diploid (2n).
In angiosperms the endosperm results from triple fusion (2 polar nuclei + 1 sperm) → triploid (3n), not diploid.
Because endosperm is not diploid, option (d) 'All of these' cannot be correct; the unambiguously diploid structure is the zygote.