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

DNA replication occurs during the S phase, or synthesis phase, of the cell cycle. This phase is crucial because it is when the cell synthesizes a complete set of DNA, allowing for the genetic material to be duplicated in preparation for cell division. Each chromosome is replicated to produce two sister chromatids, ensuring that both daughter cells will receive an identical set of chromosomes.

In the context of the cell cycle, the S phase follows the G1 phase, where the cell grows and carries out normal functions but does not yet copy its DNA. It is also before the G2 phase, where the cell continues to grow and prepares for mitosis, including the synthesis of proteins necessary for cell division. The M phase, or mitosis, is the process during which the cell divides and distributes the replicated chromosomes to daughter cells but does not involve DNA replication itself. Thus, the only phase explicitly dedicated to the replication of DNA is the S phase.