Which phase of the cell cycle is characterized by DNA replication?

• A. G1 phase
• B. S phase
• C. G2 phase
• D. M phase

Answer: (B)

The S phase, or synthesis phase, of the cell cycle is specifically designated for DNA replication. During this phase, the entire genome is duplicated in preparation for cell division. This ensures that when the cell divides, each daughter cell receives an identical set of chromosomes.

In the G1 phase, which occurs prior to the S phase, the cell grows and carries out normal metabolic processes, but DNA replication has not yet begun. The G2 phase follows the S phase, where the cell continues to grow and produces the proteins necessary for mitosis, but again does not involve the replication of DNA. The M phase is the mitotic phase where the cell divides into two daughter cells; the genetic material has already been replicated by this point.

Thus, the S phase is uniquely distinct for the process of DNA replication, making it the correct choice for this question.