The spindle checkpoint
"The spindle checkpoint" is a free, interactive Class 11 Biology simulation for NEET, built on the NCERT section "Prophase and metaphase" in Cell Cycle and Cell Division. Attach spindle fibres from both poles to each kinetochore; anaphase cannot fire until every chromosome is bi-oriented on the metaphase plate, then all centromeres split at once and centromeres lead to the poles. NEET has asked about this idea 7 times in 10 years of papers.
From the lesson Prophase and metaphase in Cell Cycle and Cell Division. Change the values and watch what happens.
What it shows
NCERT §10.2.1–10.2.3
Attach spindle fibres from both poles to each kinetochore; anaphase cannot fire until every chromosome is bi-oriented on the metaphase plate, then all centromeres split at once and centromeres lead to the poles.
Controls
3 to try
- Dragspindle fibre from a pole to a kinetochore
- Toggleanaphase-promoting complex working / defective
- Buttontry to start anaphase
Try this
Bi-orient all four chromosomes so anaphase starts, then break the APC and predict what the cell does.
Common mistake
Chromosome number doubles at S rather than at centromere split; kinetochores attach to one pole only.
In NEET
10 years of papers
Asked 7 times in 10 years of NEET.
See the past questions: Cell Cycle and Cell Division (chapter)
The idea behind it
NCERT §10.2.1–10.2.2
- Mitosis is called equational division because parent and daughter cells have the same number of chromosomes. Its nuclear division (karyokinesis) is split into four stages, prophase, metaphase, anaphase and telophase, but the process is continuous and the boundaries between stages are not sharp.
- Prophase follows the S and G2 phases. Straight after S and G2 the new DNA molecules are intertwined and not distinct; prophase begins as the chromosomal material starts to condense and gets untangled.
- By the end of prophase the chromosomes are compact, and each is seen to consist of two chromatids joined at the centromere.
- The centrosome, duplicated during S phase, starts moving towards opposite poles. Each centrosome sends out microtubules called asters, and the two asters with the spindle fibres form the mitotic apparatus.
- Under the microscope a cell at the end of prophase shows no Golgi complex, no endoplasmic reticulum, no nucleolus and no nuclear envelope.
- Metaphase begins with the complete disintegration of the nuclear envelope, so the chromosomes lie spread in the cytoplasm. Condensation is now complete.
- Metaphase is the stage at which chromosome morphology is easiest to study. Each metaphase chromosome is two sister chromatids held together by the centromere.
- Kinetochores are small disc-shaped structures on the surface of the centromere, where spindle fibres attach.
- All the chromosomes come to lie at the equator: one chromatid of each chromosome is attached by its kinetochore to fibres from one pole, and its sister to fibres from the other pole. The plane of alignment is the metaphase plate.
Questions
4 answers
- What does the "The spindle checkpoint" simulation show?
- Attach spindle fibres from both poles to each kinetochore; anaphase cannot fire until every chromosome is bi-oriented on the metaphase plate, then all centromeres split at once and centromeres lead to the poles.
- What mistake does the "The spindle checkpoint" simulation fix?
- A common mistake it clears up: chromosome number doubles at S rather than at centromere split; kinetochores attach to one pole only.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 7 times in 10 years of papers.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Prophase and metaphase" in Cell Cycle and Cell Division (Class 11 Biology).
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