During the cell cycle, in which phase are chromosomes most visibly condensed and distinguishable under a light microscope?

• A. S phase of interphase
• B. Prophase of mitosis
• C. G1 phase of interphase
• D. Telophase of mitosis

Answer: (B)

Verified step by step guidance

1. Understand the cell cycle phases: The cell cycle consists of interphase (G1, S, G2 phases) and mitotic phase (mitosis and cytokinesis).
2. Recall chromosome behavior during interphase: In G1 and S phases, chromosomes are not condensed; DNA is in a relaxed chromatin state to allow replication and transcription.
3. Identify chromosome condensation during mitosis: Chromosomes begin to condense and become visible under a light microscope during prophase, the first stage of mitosis.
4. Compare chromosome visibility in other mitotic phases: In telophase, chromosomes start to decondense as the cell prepares to complete division, making them less distinct.
5. Conclude that chromosomes are most visibly condensed and distinguishable under a light microscope during prophase of mitosis.