AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    The DNA replicates to form two copies of each chromosome.

    Full specification wording

    Mitosis and the cell cycle: The DNA replicates to form two copies of each chromosome.

    DNA replication occurs during interphase and produces two identical copies of every chromosome.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 4 of 9
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    DNA replication occurs during interphase and produces two identical copies of every chromosome. The DNA double helix unwinds and each strand acts as a template so that new complementary strands are built, giving two identical DNA molecules. Each chromosome therefore consists of two identical copies, often called sister chromatids, held together until mitosis separates them. For example, a human cell with 46 chromosomes replicates its DNA so that there are temporarily 92 chromatids, arranged as two copies of each of the 46 chromosomes. This ensures that when the nucleus divides, each daughter cell receives a complete and identical set of genetic information.

    What earns the marks

    • States that DNA replication happens during interphase before mitosis.
    • Describes the formation of two identical copies of each chromosome.
    • Explains that the copies are identical because each is made from the original DNA template.
    • Links DNA replication to the production of genetically identical daughter cells.
    • Uses the idea that each daughter cell receives one copy of every chromosome.

    Common mistakes and how to put them right

    • Saying the chromosome number doubles permanently.

      Put it right by explaining that the copies are separated during mitosis so each daughter cell has the original number.

    • Confusing replication with transcription.

      Put it right by stating that replication copies the whole DNA molecule, whereas transcription makes RNA from a gene.

    • Thinking new chromosomes are made from scratch.

      Put it right by describing copies made from the original DNA strands.

    Exam tips

    • State clearly that replication happens in interphase, before mitosis.
    • Use the phrase two identical copies of each chromosome to match the specification wording.
    • Explain the consequence: identical copies allow identical daughter cells to form.

    Try the lesson

    The start of the Mitosis and the cell cycle: The DNA replicates to form two copies of each chromosome. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What does DNA replication produce?

    Listen

    DNA replication occurs during interphase and produces two identical copies of every chromosome. The DNA double helix unwinds and each strand acts as a template so that new complementary strands are built, giving two identical DNA molecules. Each chromosome therefore consists of two identical copies, often called sister chromatids, held together until mitosis separates them. For example, a human cell with 46 chromosomes replicates its DNA so that there are temporarily 92 chromatids, arranged as two copies of each of the 46 chromosomes. This ensures that when the nucleus divides, each daughter cell receives a complete and identical set of genetic information. A strong answer earns marks for these points. States that DNA replication happens during interphase before mitosis. Describes the formation of two identical copies of each chromosome. Explains that the copies are identical because each is made from the original DNA template. Links DNA replication to the production of genetically identical daughter cells. A common slip: Saying the chromosome number doubles permanently. Instead, explaining that the copies are separated during mitosis so each daughter cell has the original number. Exam tip: State clearly that replication happens in interphase, before mitosis.

    See it

    A top-down flowchart with seven boxes linked by arrows. The first box says DNA replicates during interphase and points to a second box saying two identical copies of each chromosome. From this second box two arrows lead out: one to a box saying the copies are identical because each is made from the original DNA template, and one to a box saying the copies are held together until mitosis separates them. The separation box leads to a box saying the nucleus divides, which leads to a box saying each daughter cell receives one copy of every chromosome, which finally leads to a box saying genetically identical daughter cells.
    It shows DNA replication in interphase producing two identical copies of each chromosome, which mitosis then separates so each daughter cell receives one copy of every chromosome.

    Key words

    Say what each word means before you turn the card.

    DNA replication

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    Chromosome copies

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    Interphase

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    Genetic identity

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    See every definition
    DNA replication
    The DNA replicates to form two copies of each chromosome, happening during interphase before mitosis.
    Chromosome copies
    Each chromosome consists of two identical copies, often called sister chromatids, held together until mitosis separates them.
    Interphase
    The stage of the cell cycle during which DNA replication happens, before mitosis.
    Genetic identity
    Replication ensures that when the nucleus divides, each daughter cell receives a complete and identical set of genetic information.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart with seven boxes linked by arrows. The first box says DNA replicates during interphase and points to a second box saying two identical copies of each chromosome. From this second box two arrows lead out: one to a box saying the copies are identical because each is made from the original DNA template, and one to a box saying the copies are held together until mitosis separates them. The separation box leads to a box saying the nucleus divides, which leads to a box saying each daughter cell receives one copy of every chromosome, which finally leads to a box saying genetically identical daughter cells.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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