Question

Before cell division, the entire DNA content of the cell gets doubled during interphase. This doubling takes place :

• A. Somewhere during the middle of the interphase
• B. Throughout the interphase
• C. At the beginning of the interphase
• D. At the end of the interphase

Answer 1

The correct option is A Somewhere during the middle of the interphase

The interphase is divided into three further phases:
• $G_1$ phase (Gap 1)
• $S$ phase (Synthesis)
• $G_2$ phase (Gap 2)

During $G_1$ phase the cell is metabolically active and continuously grows but does not replicate its DNA.

S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. If the initial amount of DNA is denoted as $2C$ then it increases to $4C$. However, there is no increase in the chromosome number; if the cell had diploid or $2n$ number of chromosomes at $G_1$, even after $S$ phase the number of chromosomes remains the same, i.e., $2n$.

During the $G_2$ phase, proteins are synthesised in preparation for mitosis while cell growth continues.

So, the correct answer is "option D"