DNA Synthesis: Cell Cycle Phase

Correct Answer: S-phase

DNA synthesis/replication occurs in the S-phase (Synthesis phase) of Interphase in the cell cycle.

Interphase Stages

• G1 phase: Cell growth; protein synthesis; preparation for DNA replication
• S phase (Synthesis): DNA replication ✔ — each chromosome is duplicated into two sister chromatids
• G2 phase: Further growth; preparation for mitosis/meiosis

Connection to Crossing Over (from notes)

After DNA replication in S-phase, the duplicated homologous chromosomes pair up in Prophase-I of Meiosis. Crossing over — exchange of segments between non-sister chromatids of homologous chromosomes — occurs specifically in the pachytene stage of Prophase-I. It is the 2nd biggest cause of genetic variation (after segregation).