Question: 122 Among eukaryotes, replication of DNA takes place in –
(1) G_{1} phase
(2) \mathrm{G}_{2} phase
(3) M phase
(4) S phase
Answer: Option (4)
Explanation:
The eukaryotic cell cycle consists of interphase and M phase.
Interphase is divided into G_{1}, S, and G_{2} phases.
During the S phase, also called the synthesis phase, DNA replication occurs,
resulting in duplication of chromosomes.
In the G_{1} phase, the cell grows and prepares for DNA synthesis,
while in the G_{2} phase, the cell prepares for mitosis.
M phase involves division of the nucleus and cytoplasm and does not involve DNA replication.
Hence, DNA replication among eukaryotes takes place in the S phase,
making Option (4) the correct answer.