In which phase of the cell cycle does DNA replication occur?

DNA replication occurs during the interphase of the cell cycle, which is the phase where the cell prepares for division and ensures that it has two complete sets of DNA to pass on to the daughter cells. Specifically, the S phase (Synthesis phase) is a part of interphase where the actual replication of DNA takes place. During this phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome, which are essential for proper segregation during cell division.

Interphase encompasses three distinct subphases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2). G1 and G2 are primarily focused on cell growth and preparation for DNA synthesis and mitosis, respectively. Therefore, defining the correct answer as interphase captures the entire preparation phase leading to DNA replication.