In the context of DNA replication and the cell cycle, during which phase do chromosomes duplicate (i.e., DNA is replicated) before mitosis begins?

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

Answer: (B)

Verified step by step guidance

1. Understand that the cell cycle consists of several phases: G1 (first gap), S (synthesis), G2 (second gap), and M (mitosis).
2. Recognize that DNA replication, or chromosome duplication, occurs during the S phase, which is part of interphase, before mitosis begins.
3. Recall that during metaphase, prophase, and telophase, the cell is undergoing mitosis, where chromosomes are already duplicated and being separated.
4. Therefore, identify the S phase as the specific phase where DNA synthesis and chromosome duplication take place.
5. Summarize that chromosomes duplicate during the S phase of interphase, preparing the cell for the subsequent mitotic phases.