Each chromosome carries two sister kinetochores that independently run a stochastic search-and-capture cycle: an unattached kinetochore has a random per-frame chance of being captured by a passing microtubule from either spindle pole. Only when both sisters end up attached to opposite poles (amphitelic) does the centromere stretch and generate tension — Aurora B senses the absence of tension on any other outcome (unattached, or both sisters syntelic to the same pole) and releases that fiber to re-try, exactly as it does in a real cell.
Per-kinetochore state machine (per animation frame, dt seconds):
unattached --P(capture)=1-e^(-captureRate·dt)--> attached to a pole
attached, no tension --P(release)=1-e^(-corrRate·dt)--> unattached (retry)
attached, opposite poles (tension) --> stable, locked in
SAC gate (global, per chromosome pair):
anaphase blocked while ANY chromosome lacks tension
onset time = time of the SLOWEST (last-to-biorient) chromosome
- Chromosomes — how many sister-chromatid pairs sit on the metaphase plate.
- Erroneous-capture rate — chance a kinetochore is captured by the same pole its sister already holds (syntelic error) rather than a free random pole.
- Microtubule capture rate — how often an unattached kinetochore rolls the dice for a new capture attempt.
- Aurora B correction rate — how fast a tension-less attachment is released and sent back to search.
- Checkpoint override — simulates a drugged or mutant SAC: anaphase fires on a fixed timer regardless of attachment state, so whichever kinetochores are still unattached or syntelic get dragged to the wrong pole. Compare its mis-segregation rate against the checkpoint-respecting run in the trial statistics panel — the checkpoint-respecting run converges on essentially zero mis-segregation because it always waits for the slowest kinetochore; the override run does not.
Real cells hold anaphase for minutes to hours until every kinetochore satisfies the checkpoint; overriding it experimentally (or through checkpoint mutations) is a direct source of chromosome mis-segregation in cancer cells and of aneuploidies such as trisomy 21.