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.
G1, S, G2, M.
It is during the G1 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 G2 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: G1,S,G2,M.