DNA replication occurs during which phase of the cell cycle?

DNA replication occurs during which phase of the cell cycle?

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

Answer: (B)

DNA replication happens during the S phase of the cell cycle, the period dedicated to copying the genome. In S phase, the DNA unwinds at multiple origins of replication and each strand serves as a template to synthesize a new complementary strand, producing two identical sister chromatids for each chromosome by the end. This duplication must occur before mitosis so that each daughter cell receives a complete set of chromosomes. The other phases serve for growth and preparation: G1 is for cell growth and checking conditions, G2 finishes preparation and checks for DNA errors, and M phase is when chromosomes condense and are separated into new cells.

DNA replication happens during the S phase of the cell cycle, the period dedicated to copying the genome. In S phase, the DNA unwinds at multiple origins of replication and each strand serves as a template to synthesize a new complementary strand, producing two identical sister chromatids for each chromosome by the end. This duplication must occur before mitosis so that each daughter cell receives a complete set of chromosomes. The other phases serve for growth and preparation: G1 is for cell growth and checking conditions, G2 finishes preparation and checks for DNA errors, and M phase is when chromosomes condense and are separated into new cells.