Cell Cycle

Interphase, the period between two successive cell divisions, is divided into three sub-phases that prepare the cell for division. DNA replication, during which the genetic material is copied so that the amount of DNA per cell doubles, occurs exclusively in the S or synthesis phase, as set out in NCERT Class 11, Chapter 10 (Cell Cycle and Cell Division). The G1 phase is incorrect because it is the interval of growth and metabolic activity before DNA synthesis begins, during which the DNA content stays unchanged. The G2 phase is also wrong, since it follows replication and involves further growth and synthesis of proteins needed for mitosis, with the DNA already doubled but not being copied again. The M phase is the stage of actual division and segregation of chromosomes, not of DNA duplication. A quantitative sanity check supports the answer: if a diploid cell begins with a 2C amount of DNA, that amount rises to 4C only after the synthesis phase, confirming that replication is confined to the S phase of interphase.