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

DNA replication occurs during the S phase, also known as the Synthesis phase, of the cell cycle. During this phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome. This is a critical process because it ensures that when a cell divides, each daughter cell receives an identical set of chromosomes, maintaining genetic continuity.

Prior to the S phase, during the G1 phase, the cell grows and prepares for DNA replication but does not yet replicate its DNA. After the S phase, in the G2 phase, the cell continues to grow and produces proteins necessary for mitosis, but DNA replication has already been completed. The M phase involves the actual division of the cell into two daughter cells and does not involve DNA replication. Thus, S phase is specifically designated for this crucial process of DNA synthesis, reinforcing its importance in the overall cell cycle.