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Mitosis and chromosome number

Distinguish between the number of chromosomes and the relative amount of DNA based on the centromere.

    B04 · Mitosis and chromosome numberReady
    Distinguish between the number of chromosomes and the relative amount of DNA based on the centromere. You can also experiment with the numbers and controls below.

    Life sciences, cells, and material movement / principles and exploration

    Mitosis and chromosome number — principles and investigation

    To understand mitosis, we need to count the number of chromosomes and the amount of DNA separately. Explore the stages of division in sequence, connecting DNA replication, separation of sister chromatids, and daughter cell formation. Counting chromosomes by centromere can account for differences immediately after replication and immediately after separation.

    How does it work?

    In S phase, DNA is copied from 2 to 4, but the number of chromosomes is the same. The total number of chromosomes in the anaphase cell doubles, and each daughter cell returns to its original number and DNA relative amount of 2.

    Key relationship

    The number of chromosomes is based on the centromere. The amount of DNA is relative.

    Try this investigation

    1. Observe the order of interphase G1 → S → G2 and division. Compare the stopped scenes with the previous and next division level buttons and arrange the lower level buttons in order.
    2. Run and record the entire division of 2n=4. We count the centromere as one chromosome and do not count the two replicated arms of X as separate chromosomes.
    3. Select only 2n=6 and record the same division process. Since the G1 DNA in each selection is normalized to 2, this value does not compare the absolute DNA masses of the two selections.

    Interpreting your results

    At 2n=4, what are the total number of chromosomes and relative amounts of DNA in the anaphase cell?

    In anaphase, the centromeres of sister chromatids are separated and each is counted as a chromosome. Since no new DNA is synthesized, the total DNA of the cell is 4, the same as G2. There are 4 DNA 2 at one pole.

    Assumptions and limitations

    It is a simple step model of one normal somatic cell with 2n=4 or 6. Chromosomes are the relative amount of G1 DNA = 2 for each selection, based on the centromere. In prophase and anaphase, the nuclear membrane disintegrates, so the value per nucleus is not defined. Telophase differentiates the entire cell before division and two new nuclei, and cytokinesis is based on one daughter cell. Stage times and chromosome shapes are staged and do not cover actual cell cycle times, division errors, or meiosis.