The Cell Cycle and Events of M-Phase

ID #1310

In one of our lectures, there was the graph of the cell cycle, can you explain it? Well, actually the only parts I can identify is that 2n is for diploid and that G2 has 2 times more DNA than G1 because G2 occurs right after S phase where DNA is synthesized, but I don't understand why G2+M has a smaller peak than G1 and why G2+M is 4n while G1 is 2n, diploid.

G2 and M together have a smaller peak than G1 under these experimental conditions because the cells are spending about half the time in either G2 or M that they spend in G1. Since there are hundreds or thousands of cells in this experiment, and each one is in its own part of the cell cycle independently of its neighbors, the probability is that more cells will be in G1, since they spend longer in that phase. So the peak is higher where you find more cells.

You answered your second question yourself. G2 + M are labeled 4n because you have finished DNA replication. Since you started DNA replication with a 2n amount of DNA, you finish replication (S-phase) with 2 x 2n = 4n amount of DNA.

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