Question: During the cell cycle, why is the change in DNA content from 2n to 4n gradual, but the change from 4n to 2n is abrupt? Multiple Choice DNA replication happens quickly in S phase, whereas cell division happens gradually over M phase. DNA replication happens quickly in M phase, whereas cell division happens gradually over S phase. DNA replication happens gradually over S phase, whereas cell division happens quickly in M phase. DNA replication happens gradually over M phase, whereas cell division happens quickly in S phase.