Question

This graph is a typical cell cycle representing DNA content of various phases (1 to 4). Identify the phases based on changes in the DNA content and select the correct option.

• A. M, G${}_1$, S, G${}_2$.
• B. G${}_2$, M, G${}_1$, S.
• C. S, G${}_2$, M, G${}_1$.
• D. G${}_1$, S, G${}_2$, M.

Answer 1

The correct option is D

G${}_1$, S, G${}_2$, M.

It is during the $G_1$ phase that the DNA content is equal to 2C, as indicated by the portion marked as 1 in the graph. S phase is regarded as replication stage where content begins doubling and the beginning of $G_2$ phase marks the completion of replication of DNA, where the content doubles to 4C. Therefore, these are represented by the areas 2 and 3 in the graph. During M (mitosis) stage, the content gets halved and distributed between the daughter cells and it becomes 2C again, which is 4 in the graph. Thus, the correct option is D: $G_1,S,G_2,M$.