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

DNA replication occurs during the S phase of the cell cycle. The S phase, or synthesis phase, is specifically designated for the duplication of the cell's DNA. This is essential for cell division, as it ensures that each daughter cell receives an identical set of chromosomes. During this phase, the DNA unwinds and separates, allowing enzymes called DNA polymerases to synthesize new strands complementary to the original ones, resulting in two identical copies of the genome.

In the G1 phase, the cell is primarily focused on growing and producing proteins necessary for DNA synthesis, but no replication occurs during this stage. The M phase, or mitotic phase, is when the cell divides its already replicated DNA into two daughter cells, but this phase does not involve replication itself. The G2 phase involves the preparation for mitosis, where the cell continues to grow and produces additional proteins and organelles, but again, there is no DNA replication taking place during this phase. Hence, the S phase is uniquely responsible for DNA replication in the cell cycle.