Q.29 Chromosome duplication during the cell cycle occurs in
(A) G1 phase
(B) G2 phase
(C) M phase
(D) S phase

Chromosome duplication occurs during the S phase of the cell cycle. This is a key concept in cell biology for exams like CSIR NET Life Sciences. The correct answer is (D) S phase.​

Question Breakdown

The query asks: “Chromosome duplication during the cell cycle occurs in (A) G1 phase (B) G2 phase (C) M phase (D) S phase.” Chromosome duplication refers to DNA replication, where each chromosome forms two sister chromatids.​

Option Analysis

• G1 Phase: Cell grows, synthesizes proteins, and checks for DNA damage, but no DNA replication happens.​

• G2 Phase: Cell prepares for mitosis with cytoplasmic growth and DNA repair after replication, but duplication is already complete.​

• M Phase: Involves mitosis (chromosome segregation) and cytokinesis; chromosomes condense and separate, no duplication.​​

• S Phase: DNA synthesis duplicates chromosomes via replication, doubling DNA content from 2C to 4C while chromosome number stays the same.​

The cell cycle ensures precise chromosome duplication cell cycle S phase events for growth and division. In chromosome duplication during cell cycle, DNA replication defines the S phase.​

Cell Cycle Overview

Eukaryotic cells follow interphase (G1, S, G2) and M phase. Interphase prepares for division; chromosome duplication cell cycle happens only once per cycle.​

S Phase: Core of Duplication

During S phase, DNA polymerase replicates each strand, forming sister chromatids joined at centromeres. Centrioles duplicate too. This maintains genetic fidelity.​

• DNA content doubles (2C to 4C).

• Regulated by cyclin-CDK complexes.

• Checkpoints prevent errors.​

Why Not Other Phases?

G1 focuses on growth; G2 on repair; M on segregation. Errors here lead to aneuploidy.​​

CSIR NET Relevance

This topic tests integration of molecular biology and cell cycle regulation. Practice: “DNA replication occurs in S phase prior to mitosis”.​