Mitotic cell cycle is divided typically into four phases, $G_1$, S, $G_2$ and M. Considering a mitotic cycle time of $18$ hours, the distribution of period of time(in hours) for each of these phase will be. $G_1$S${}_2$M.

If the cell cycle is restricted in $G_1$ phase of cell, the condition is known as

If the cell cycle is restricted in $G_1$ phase of cell, the condition is known as -

During which phase(s) of cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C?