During the S phase of the cell cycle. DNA replication occurs when the cell duplicates its chromosomes in preparation for division, and this happens after G1 and before G2.

• G1: Cell growth and preparation for DNA synthesis.
• S: DNA replication dupl icates the genome.
• G2: Final preparations for mitosis and quality control.
• M: Mitosis and cytokinesis divide the cell.

If you’d like, I can provide a succinct one-line study prompt or a short diagram-like description to help memorize the sequence.