Q. 7 - Biology

Question

Chromosomes are duplicated during what stage of the cell cycle?

a. G1 phase

b. S phase

c. prophase

d. prometaphase 

Step-by-Step Solution

Answer

The correct answer is (b) S phase.

Step 1. Introduction

Cell cycle is series of events that take place in a cell that causes it to divide into two daughter cells. The eukaryotic cell consists of 4 distinct phases:

$G_1$ phase

S phase

$G_2$ phase

M phase

Step 2. G1 phase

It is an intermediate phase. During this time cell grows in preparation for DNA replication, and certain intracellular components such as centrosomes undergo replication.

Step 3. S phase

It is responsible for the synthesis or replication of DNA i.e. duplication of chromosomes takes place in this phase.

Step 4. Prophase

In this step homologous chromosomes form bivalents and crossing over occurs between non-sister chromatids.

Step 5. Prometaphase

In this chromosomes continue to condense and kinetochores appear at the centromeres. The mitotic spindle attach to kinetochores and the centrosomes move toward opposite poles.