Cell Cycle

AP Biology· difficulty 2/5

Synchronized human cells were grown and DNA content per cell was measured by flow cytometry. The histogram shows the distribution of cells by DNA content (1n vs 2n).

DNA content # cells 2N 4N

Cells in the central plateau are most likely in which phase?

  • A

    G1 phase

  • B

    G2 phase

  • C

    Mitosis

  • D

    S phase (DNA replication in progress)

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Explanation

Cells with intermediate DNA content (between 2N and 4N) are actively replicating DNA, defining S phase. The two peaks correspond to G1 (2N) and G2/M (4N).

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