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DNA Repair in the Cell Cycle


The typical eukaryotic cell cycle, shown in the figure below, includes two major phases: the M phase (mitosis and cytokinesis), in which the cell first separates its chromosomes into two groups and then divides into two daughter cells; and the I phase (interphase) between M phases. Interphase has three subphases, in sequential order:

• The G1 phase (for “Gap 1”) begins following cytokinesis (cell division) and is usually the longest phase of the three. The cell will grow in size and conduct its usual metabolic activities.

• During the S phase (for “Synthesis”) the DNA is replicated. The cell will have two identical copies of all of the chromosomes following this phase.

• The G2 phase (for “Gap 2”) occurs between DNA synthesis and mitosis. The cell will continue to grow and will prepare for mitosis.

Schematic of the cell cycle. outer ring: I = Interphase, M = Mitosis; inner ring: M = Mitosis, G1 = Gap 1, G2 = Gap 2, S = Synthesis; not in ring: G0 = Gap 0/Resting. Wheeler, Richard. Schematic Representation of the Cell Cycle. Digital image. Wikipedia, 25 Jan. 2011. Web. 5 Feb. 2016.

Reviewing the phases and subphases of the cell cycle described above. Which phase would be the most appropriate for DNA repair mechanisms to detect and repair damage to DNA?


The M phase.


The G1 phase.


The S phase.


The G2 phase.