Q.18 During eukaryotic cell division, the amount of DNA doubles
(A) between prophase and anaphase of mitosis
(B) between prophase I and prophase II of meiosis
(C) between the G1 and G2 phases of the cell cycle
(D) during the M phase of the cell cycle

The correct answer is (C) between the G1 and G2 phases of the cell cycle.

DNA replication occurs specifically during the S (synthesis) phase, which lies between G1 and G2, doubling the DNA content from 2C (G1) to 4C (G2).

Option Analysis

(A) Between prophase and anaphase of mitosis
No DNA replication happens during mitosis; chromosomes condense in prophase and separate in anaphase, but DNA content remains constant at 4C throughout M phase.

(B) Between prophase I and prophase II of meiosis
DNA replicates only once before meiosis I (in S phase), so content stays at 4C from prophase I through meiosis I reduction division to prophase II—no doubling occurs here.

(C) Between the G1 and G2 phases of the cell cycle
Correct: G1 has 2C DNA; S phase replication doubles it to 4C by G2, preparing for division.

(D) During the M phase of the cell cycle
M phase involves chromosome segregation and cytokinesis, not replication; DNA amount per cell halves post-division.

In eukaryotic cell division, understanding when the amount of DNA doubles is crucial for CSIR NET Life Sciences aspirants tackling cell cycle questions. The DNA content doubles precisely between the G1 and G2 phases of the cell cycle through replication in the S phase, ensuring each daughter cell receives an identical genome.

This process underpins mitosis and meiosis, preventing errors in genetic inheritance.

Cell Cycle Phases Breakdown

• G1 Phase: Cell growth with 2C DNA content; no replication.

• S Phase: DNA synthesis doubles content to 4C via semi-conservative replication.

• G2 Phase: Preparation for mitosis with replicated 4C DNA.

• M Phase: Division without further doubling.

Common MCQ Traps

Options like prophase-anaphase or M phase confuse segregation with replication, while meiosis intervals overlook single pre-meiotic replication.

Focus on S phase for CSIR NET success in molecular biology sections.