DNA Replication in the S Phase

Steps:

• Recall the cell cycle phases: interphase (G1, S, G2) and mitosis (M).
• Identify interphase as the preparation stage before division.
• Note S phase within interphase as the synthesis period.
• Confirm DNA replication doubles genetic material specifically in S phase.

Why D is correct:

• S phase is defined as the synthesis stage where DNA replication occurs to ensure each daughter cell gets a full genome copy.

Why the others are wrong:

• A. G1: Focuses on cell growth and organelle synthesis, before DNA replication.
• B. G2: Involves growth and checkpoint verification after replication, not during it.
• C. M: Mitosis phase divides the nucleus and cytoplasm, using already replicated DNA.

Final answer: D