What Is Mitosis? Why It Is Called Equational Division
Biology · Cell Cycle and Cell Division · NEET
Mitosis is the M phase of the cell cycle. One parent cell divides into two daughter cells. It is called "equational division" because the chromosome number stays equal — a diploid (2n) cell makes two diploid (2n) daughter cells with the same DNA. Memory hook: "Equational = Equal number." Parent 2n → two cells, each still 2n.
In mitosis a diploid parent cell (2n = 46, 4C after S phase) divides once into two daughter cells that each keep the same chromosome number (2n = 46, 2C). The chromosome number stays equal, which is why mitosis is called equational division.
Your doubts, answered
Why exactly is mitosis called "equational" division?
Because the chromosome number in the parent cell and in each daughter cell is the SAME (equal). NCERT states: "Since the number of chromosomes in the parent and progeny cells is the same, it is also called as equational division." A cell with 2n = 46 chromosomes makes two cells that each also have 46. The number is not reduced, so it is equational, not reductional.
Does the chromosome number change during mitosis? (2n → 2n or 2n → n?)
It stays the same: 2n → 2n. In the S phase before mitosis, DNA doubles (2C → 4C), but the chromosome NUMBER does not change during mitosis. At anaphase the centromere splits and the two chromatids of each chromosome move to opposite poles, so each daughter cell ends up with the same number of chromosomes as the parent. Only meiosis reduces the number (2n → n).
What is the difference between equational and reductional division?
Equational division (mitosis, and also Meiosis II) keeps the chromosome number equal to the parent. Reductional division (Meiosis I) halves the chromosome number from diploid (2n) to haploid (n) by separating homologous chromosomes. Trap point: Meiosis I is reductional; Meiosis II is equational because it separates sister chromatids like mitosis does.
Do the daughter cells have the same DNA as the parent?
Yes. Mitosis produces two genetically identical daughter cells with the same genetic complement as the parent. There is no synapsis, no crossing over, and no pairing of homologous chromosomes in mitosis — so no genetic variation is introduced. This is why mitosis is used for growth and repair, where identical copies are needed.
Is mitosis only for diploid cells?
Usually yes. NCERT says mitosis (equational division) is "usually restricted to the diploid cells only." But in some lower plants and some social insects (like haploid drones in bees), haploid cells can also divide by mitosis. So the exact NCERT line for NEET is "usually restricted to diploid cells" — not "only diploid cells."
⚠️ The NEET trap ✗ Mitosis is equational because the DNA amount stays the same in parent and daughter cells. ✓ Mitosis is equational because the CHROMOSOME NUMBER stays the same (2n → 2n). DNA amount actually changes: it is 4C in the parent cell (after S phase) and each daughter gets 2C. The word "equational" refers to equal chromosome number, not equal DNA content. 🧠 "Equational" is about NUMBER, not DNA amount.
Real NEET questions
2023
Match List I with List II:
List I: A. M Phase B. G2 Phase C. G1 Phase (quiescent) D. G1 Phase
List II: I. Proteins are synthesized II. Inactive phase III. Interval between mitosis and initiation of DNA replication IV. Equational division
A · A-III, B-II, C-IV, D-I
B · A-IV, B-II, C-I, D-III
C · A-IV, B-I, C-II, D-III ✓
D · A-II, B-IV, C-I, D-III
Solution: M phase is the equational division (A-IV). During G2 phase proteins are synthesised for mitosis (B-I). The quiescent/G0 stage is the inactive phase (C-II). G1 phase is the interval between mitosis and the start of DNA replication (D-III). So the answer is A-IV, B-I, C-II, D-III.
2022
Which one of the following never occurs during mitotic cell division?
A · Spindle fibres attach to kinetochores of chromosomes
B · Movement of centrioles towards opposite poles
C · Pairing of homologous chromosomes ✓
D · Coiling and condensation of the chromatids
Solution: Pairing (synapsis) of homologous chromosomes is a meiotic event (zygotene of prophase I) and never occurs in mitosis. Because there is no pairing or crossing over, mitosis stays equational and produces identical daughter cells. The other three events all happen normally in mitosis.
2016
Which of the following is not a characteristic feature during mitosis in somatic cells?
A · Spindle fibres
B · Disappearance of nucleolus
C · Chromosome movement
D · Synapsis ✓
Solution: Synapsis (pairing of homologous chromosomes) is specific to meiosis (zygotene) and does not occur in mitosis. Spindle fibres, disappearance of the nucleolus, and chromosome movement are all normal mitotic features. Absence of synapsis is why mitosis keeps chromosome number equal and produces identical cells.
Solved Cell Cycle and Cell Division NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mitosis is the M phase of the cell cycle in which one cell divides into two genetically identical daughter cells with the same chromosome number as the parent.
Why is mitosis called equational division?
Because the chromosome number of the parent and each daughter cell is equal (the same). A 2n cell gives two 2n cells, so the number is not reduced.
What is the chromosome number change in mitosis?
2n → 2n. The number does not change. Only the DNA content per cell changes: 4C parent gives 2C in each daughter after division.
Is Meiosis I equational or reductional?
Meiosis I is reductional (2n → n). Meiosis II is equational, like mitosis, because it separates sister chromatids without reducing chromosome number.
Which cells undergo mitosis?
Mitosis is usually restricted to diploid cells, but in some lower plants and some social insects (like haploid honeybee drones), haploid cells can also divide by mitosis.
