Spindle Fibres and Kinetochore: How Chromosomes Are Moved
Biology · Cell Cycle and Cell Division · NEET
Spindle fibres attach to the kinetochore, a small disc-shaped structure on the surface of the centromere. When these fibres shorten, they pull the chromosomes to opposite poles of the cell. Memory hook: the kinetochore is the "hook", the centromere is the "wall" it sits on, and the spindle fibre is the "rope" that pulls.
Spindle fibres (microtubules) attach to kinetochores, the disc-shaped structures on the surface of the centromere, and shorten to pull chromatids toward the poles. Note: the fibre docks on the kinetochore, never directly on the centromere.
Your doubts, answered
Do spindle fibres attach to the centromere or the kinetochore?
They attach to the KINETOCHORE, not directly to the centromere. NCERT says: 'Small disc-shaped structures at the surface of the centromeres are called kinetochores. Spindle fibres attach to kinetochores of chromosomes.' The kinetochore sits ON the centromere. Writing 'spindle fibres attach to the centromere' is the classic NEET wrong option (NEET 2022 marked exactly this as the incorrect statement).
What is the difference between centromere and kinetochore?
The centromere is the constricted region that holds the two sister chromatids together. The kinetochore is a small disc-shaped protein structure that forms ON the surface of the centromere. Think of the centromere as the platform and the kinetochore as the docking plate for spindle fibres. One centromere carries the kinetochores where microtubules attach.
How do chromosomes actually move to the poles?
The spindle fibres (microtubules) are attached to kinetochores. During anaphase the centromere splits, and the kinetochore-attached microtubules SHORTEN, pulling the daughter chromatids (now daughter chromosomes) toward opposite poles. NCERT: chromosomes move 'by shortening of microtubules attached to kinetochores.' No new pushing force lifts them; the shortening rope pulls.
Where do the spindle fibres come from?
In animal cells, the centrioles form the basal body and spindle fibres that build the spindle apparatus. Each centrosome radiates microtubules called asters; the two asters together with the spindle fibres form the mitotic apparatus. Plant cells lack centrioles but still form a spindle.
Kinetochore vs kinetosome — are they the same?
No. This is a NEET trap word pair. Kinetochore = disc on the centromere where spindle fibres attach. Kinetosome (basal body) = structure at the base of cilia/flagella. In 'Spindle fibres attach on to...' (NEET 2016) the answer is kinetochore, and kinetosome is the trap option.
At which stage do spindle fibres attach to kinetochores?
At METAPHASE the kinetochores serve as the attachment sites for spindle fibres, and chromosomes align on the metaphase plate. NEET 2024 asked this directly and the answer is Metaphase. Attachment happens at metaphase; the pulling (shortening) happens at anaphase.
⚠️ The NEET trap ✗ Spindle fibres attach directly to the centromere of the chromosome. ✓ Spindle fibres attach to the kinetochore, a disc-shaped structure ON the surface of the centromere. 🧠 Centromere is the wall; the kinetochore is the hook drilled into it. The rope (spindle fibre) grabs the hook, never the bare wall. NEET 2022 marked 'attach to centromere' as the INCORRECT statement.
Real NEET questions
2016
Spindle fibres attach on to:
A · Telomere of the chromosome
B · Kinetochore of the chromosome ✓
C · Centromere of the chromosome
D · Kinetosome of the chromosome
Solution: Spindle fibres attach to the kinetochores, small disc-shaped structures on the surface of the centromere. Kinetosome is the trap (it is the basal body of cilia/flagella), and centromere only carries the kinetochore.
2022
Select the incorrect statement with reference to mitosis:
A · All the chromosomes lie at the equator at metaphase
B · Spindle fibres attach to centromere of chromosomes ✓
C · Chromosomes decondense at the telophase stage
D · Splitting of centromere occurs at anaphase
Solution: The incorrect statement is that spindle fibres attach to the centromere. They actually attach to the kinetochores on the surface of the centromere. The other three statements are correct as per NCERT.
2024
Spindle fibres attach to kinetochores of chromosomes during
A · Metaphase ✓
B · Anaphase
C · Telophase
D · Prophase
Solution: At metaphase the kinetochores serve as the sites where spindle fibres attach, aligning chromosomes on the metaphase plate. Anaphase is when these fibres shorten and pull the chromatids apart.
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.
A small disc-shaped protein structure on the surface of the centromere where spindle fibres attach.
What is the main function of spindle fibres during mitosis?
To separate the chromosomes. They attach to kinetochores and shorten to pull daughter chromatids to opposite poles (NEET 2025).
Do plant cells have spindle fibres without centrioles?
Yes. Plant cells lack centrioles but still form a spindle apparatus and use spindle fibres to move chromosomes.
When do spindle fibres attach and when do they pull?
They attach at metaphase and pull (by shortening) at anaphase, after the centromere splits.
Is the kinetochore made of DNA?
No. The kinetochore is a protein structure that assembles on the centromeric region; the centromere region has specialised DNA, but the kinetochore itself is proteinaceous.
