Answer: Entry into mitosis (G 2 to M transition).
- A DNA repair following ultraviolet radiation damage
- B Entry into mitosis (G<sub>2</sub> to M transition)
- C Cytokinesis and cleavage furrow formation
- D G<sub>1</sub> arrest in response to growth factor withdrawal
Correct answer: B. Entry into mitosis (G<sub>2</sub> to M transition)
Explanation: MPF (Cyclin B + Cdk1 complex) promotes entry into mitosis. It was the first cell cycle control protein discovered.
The cell cycle: G1 (growth and preparation), S (DNA replication, chromosome number stays 2n but DNA content doubles), G2 (final checks before division), and M (mitosis itself) - together, G1+S+G2 make up interphase.
Concept context
Mitosis and meiosis: how cells divide for growth, repair, and reproduction.