Question

Which of the following best describes the $DNA$ content and the number of chromosomes at the end of $S$ and $M -$ phases of the cell cycle in mitosis, if the $DNA$ con tent of the cell in the beginning of cell cycle ($G_{1}$-phase) is considered as $C$ and the number of chromosomes $2N$?

• A. $2C$ and $2N$ for $S-$ phase : $2C$ and $2N$ for $M-$ phase
• B. $2C$ and $N$ for $S-$phase : $2C$ and $N$ for $M-$ phase
• C. $2C$ and $2N$ for $S-$ phase : $C$ and $2N$ for $M-$ phase
• D. $C$ and $N$ for $S-$ phase : $C$ and $2N$ for $M-$ phase

Answer 1

Answer: (A)

$\begin{matrix}DNA&G_{1}\rightarrow&S\rightarrow&G_{2}\rightarrow&M\\ \text{content}&C&2C&2C&C\\ \text{Number}&2N&2N&4N&2N\end{matrix}$
of chromosome
During cell cycle in the $G_1$ -phase, the cellular contents excluding the chromosomes are duplicated. In $S-$ phase, each of the $46$ chromosomes is duplicated by the cell but their ploidy is not disturbed.
In $G_2-$ phase, the cell double checks the duplicated chromosomes for error, making any needed repair. In $M-$ phase, the cell division occurs.