Which phase of the cell cycle includes DNA replication?

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

Answer: (B)

DNA replication happens during the S phase of interphase. This is the part of the cell cycle where the genome is copied so that each daughter cell will receive a complete set of genetic information. During replication, the double helix unwinds and new complementary strands are synthesized, producing sister chromatids that will be separated later in mitosis. This preparation is essential before M phase, when the cell actually divides. The other phases have different roles: G1 is focused on growth and metabolic preparation, and G2 checks and readies the cell for division, ensuring DNA is intact before mitosis begins.