Which of the following statements is not true regarding the cell cycle?

• A
  $a$. During the $G_1$ phase, there is active synthesis of $RNA$ and proteins, but no change in its $DNA$ content.
• B
  $b$. In the synthesis or $S$ phase, each chromosome carries a duplicate set of genes.
• C
  $c$. During the $G_2$ phase, a cell contains double the amount $(4C)$ of $DNA$ present in the original diploid cell $(2C)$.
• D
  $d$. In the $S$-phase, a cell doubles the original diploid $(2n)$ chromosome number.