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

DNA replication occurs during the S phase of the cell cycle. This phase is specifically designated for the synthesis of DNA, where each chromosome is replicated to produce two sister chromatids. This is crucial as it ensures that when cell division occurs, each daughter cell will receive an identical set of chromosomes.

During the G1 phase, the cell is primarily focused on growth and the synthesis of proteins necessary for the next phase. The G2 phase involves further preparation for cell division, such as checking for DNA damage and ensuring that DNA has been properly replicated, but no new DNA is synthesized during this phase. The M phase, which includes mitosis and cytokinesis, is when the cell actually divides, and therefore, DNA replication must be completed beforehand during the S phase to ensure the integrity of the genetic material passed to the daughter cells.

Thus, the S phase is critical for DNA replication to occur effectively and for maintaining genetic continuity in cell division.