# Explain the role of cohesins and the spindle checkpoint in ensuring accurate chromosome segregation during mitosis.

> IB DP Biology Higher Level (2023 syllabus) — D2.1 Cell and nuclear division · Explain · 4 marks

## Mark scheme (4 marks)

1. Cohesins hold sister chromatids together along their length / at the centromere following DNA replication.
2. Cohesins are cleaved/degraded by separase at the metaphase-to-anaphase transition, allowing sister chromatids to be pulled to opposite poles.
3. The spindle (assembly) checkpoint detects unattached or incorrectly attached kinetochores and halts progression through mitosis until all chromosomes are correctly bi-orientated.
4. Unattached kinetochores generate a 'wait-anaphase' signal (via the mitotic checkpoint complex / MCC) that inhibits the anaphase-promoting complex (APC/C), preventing premature cohesin cleavage and non-disjunction.

## Key terms

- [cohesin](https://www.gradenine.co.uk/glossary/cohesin)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-the-role-of-cohesins-and-4fd5dc2a) · Published by Druglandscape Ltd.