Answer: The S- phase
Explanation: the S- phase is also called the synthesis phase which occurs during interphase. This S phase is responsible for replication of DNA, this replication begins when helicase enzymes unzips various location along the chromosome separating 2 complimentary strands of DNA into daughter cells having the same genetic make up.
Remember we said the S phase occurs during interphase, the interphase has 3 basic stages which begins with G1 (G stands for gap) phase. During this phase, the cell makes a variety of proteins that are needed for DNA replication.
The second phase being the S phase follows the G1 phase where all of the chromosomes are replicated. Following replication, each chromosome now consists of two sister chromatids as stated earlier.
The final phase is the G2 phase -During G2, the cell synthesizes a variety of proteins. Of particular significance to the cell cycle, most microtubules – proteins that are required during mitosis are produced during G2.
There is also a G0 phase- the Non-replicating cells are found in a stage of the cell cycle called G0. These cells may be quiescent (dormant) or senescent (aging or deteriorating). This is to ensure that damaged or defective DNA sequences is not passed on to daughter cells during replication in the S- phase.