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.
AP EAPCET 2024Set ap-2024-05-17-AN1 markMCQ
Q.Study the following table with reference to the meiocyte of Rice and find correct combination
S.No
Phase of Division
Event
Chromatid number
I
Anaphase I
Separation of chromatids
24
II
Prophase I
Condensation of chromosomes
12
III
Metaphase II
Microtubules attached to kinetochore
12
IV
Anaphase II
Division of centromere
24
(A) II, III
(B) II, IV
(C) I, IV
(D) I, III
›Reveal solutionSolution
Rows II and IV are correct; Anaphase I separates homologous chromosomes (not chromatids), so any row pairing Anaphase I with 'separation of chromatids' is wrong.
Concept and Intuition
Rice has 2n = 24, n = 12. After S-phase every chromosome carries two sister chromatids. In Meiosis I the homologous chromosomes (not chromatids) are pulled apart at Anaphase I. Sister chromatids remain together until Anaphase II, where the centromere splits and the two chromatids of each of the 12 chromosomes (24 chromatids in the cell) move to opposite poles.
Step-by-Step Solution
Row I — Anaphase I / 'Separation of chromatids': FALSE. Anaphase I separates homologous chromosomes; chromatids stay joined. Eliminate any option with I → rules out (C) and (D).
Row II — Prophase I / 'Condensation of chromosomes': TRUE. Chromosomes condense and pair in Prophase I.
Row IV — Anaphase II / 'Division of centromere', 24 chromatids: TRUE. Centromeres split and 24 chromatids segregate.
Row III — Metaphase II with a chromatid count of 12 is inconsistent (a haploid cell in Metaphase II holds 12 dyads = 24 chromatids), so the fully correct pair is II and IV.
Common Mistakes
Believing sister chromatids separate at Anaphase I — they separate at Anaphase II.
Confusing chromosome number with chromatid number after DNA replication.
✓Final answer
The correct option is (B) — rows II and IV.
ANSWER: B
Note
This solution was worked out by our team and cross-checked by a second independent solve. The official answer key for this question could not be confirmed, so please cross-verify with the official paper where possible.
A meiocyte is the diploid (2n) cell that undergoes meiosis — commonly termed the gamete (or spore) mother cell — and it is NOT itself a gamete. Answer: (B).
Concept and Intuition
Meiosis is the reductional division that converts a diploid (2n) cell into haploid (n) products. The diploid cell that actually enters and completes this division is called the meiocyte. Because its haploid products go on to form gametes (in animals, directly; in plants, via a gametophyte generation from spores), the meiocyte is conventionally referred to as the gamete mother cell (or, in the plant world, the spore mother cell, e.g., pollen mother cell/microsporocyte, megaspore mother cell). It is important not to confuse the meiocyte itself with the haploid gametes it eventually gives rise to — the meiocyte is diploid, and it is the cell entering meiosis, not the product.
Step-by-Step Solution
Define meiocyte: the cell in which meiosis actually occurs.
Note its ploidy: diploid (2n), since meiosis reduces ploidy from 2n to n — this rules out "haploid gametes" (option C) since gametes, by definition, are already haploid and are the products, not the meiocyte itself.
Rule out "Gametes" (option A) — gametes are the haploid end product of the process, not the cell undergoing meiosis.
Rule out "Diploid gametes" (option D) — this is a contradiction in terms; gametes are never diploid.
"Gamete mother cells" (option B) correctly captures a diploid cell whose meiotic division ultimately yields gametes — this is the standard usage for meiocyte.
Common Mistakes
Picking "haploid gametes," mistaking the meiocyte for its own end product.
Being misled by the internally contradictory distractor "diploid gametes."