If a cell at ${\mathrm{G}}_1$ phase has $2n$ chromosome and $2\mathrm{C}\hspace{0.17em}\hspace{0.17em}\mathrm{D}\mathrm{N}\mathrm{A,}$ then during $\mathrm{S }phas\mathrm{e,}$ $\mathrm{D}\mathrm{N}\mathrm{A}$ replication occurs but chromosome number remains unchanged. As a result, chromosome number remains $2\mathrm{n}$ but the quantity of $\mathrm{D}\mathrm{N}\mathrm{A}$ becomes $4\mathrm{C}$.