During which phase of the cell cycle are chromosomes replicated?

• A. G1 phase
• B. S phase
• C. M phase
• D. G2 phase

Answer: (B)

Verified step by step guidance

1. Understand the phases of the cell cycle: G1 (first gap), S (synthesis), G2 (second gap), and M (mitosis).
2. Recall that chromosome replication involves copying the DNA to ensure each daughter cell receives a complete set.
3. Identify that DNA replication specifically occurs during the S phase, where the cell synthesizes a complete copy of its DNA.
4. Note that G1 phase is primarily for cell growth and preparation for DNA synthesis, not replication itself.
5. Recognize that G2 phase involves preparation for mitosis, and M phase is when the cell divides, so replication must have already occurred.