Synthesis phase in the cell cycle is the replication of
DNA
Mitosis results in nuclear division, in which a full set of chromosomes is distributed to each of two daughter cells formed through cytokinesis, or cell division. The chromosomes are distributed to the daughter cells in such a way that they receive the exact same number of chromosomes as present in the parent cell. To accomplish this, the DNA content in the parent cell doubles up before actually dividing the cell. This doubling up of the DNA or DNA replication occurs during the S-phase (synthesis phase) of the cell cycle.