During the eukaryotic cell cycle, when does DNA replication occur?

• A. During mitosis (M phase)
• B. During the G2 phase of interphase
• C. During the G1 phase of interphase
• D. During the S (synthesis) phase of interphase

Answer: (D)

Verified step by step guidance

1. Understand the phases of the eukaryotic cell cycle: G1 phase (cell growth), S phase (DNA synthesis), G2 phase (preparation for mitosis), and M phase (mitosis).
2. Recall that DNA replication is the process of copying the entire genome to ensure each daughter cell receives a complete set of chromosomes.
3. Identify that DNA replication must occur before mitosis so that chromosomes can be properly segregated during cell division.
4. Recognize that the S phase (synthesis phase) of interphase is specifically dedicated to DNA replication, where the cell duplicates its DNA.
5. Conclude that DNA replication does not occur during mitosis (M phase), G1 phase, or G2 phase, but exclusively during the S phase of interphase.