AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Mitosis and the cell cycle: During the cell cycle the genetic material is doubled and then divided into two identical cells.

    Before a cell divides, its genetic material must be doubled so that each daughter cell receives a complete set of chromosomes.

    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Before a cell divides, its genetic material must be doubled so that each daughter cell receives a complete set of chromosomes. During interphase, DNA replication produces two identical copies of each chromosome, called sister chromatids, held together at a centromere. The amount of DNA in the nucleus is therefore doubled, although the chromosome number stays the same. In mitosis, the sister chromatids are separated so that one copy of each chromosome goes into each new nucleus. Cytokinesis then divides the cytoplasm, forming two genetically identical daughter cells with the same chromosome number as the parent.

    For example: A human body cell with 46 chromosomes replicates its DNA and divides by mitosis to produce two cells that each have 46 chromosomes.

    What earns the marks

    • DNA replication occurs during interphase, doubling the genetic material before division.
    • Each replicated chromosome consists of two identical sister chromatids joined at a centromere.
    • The chromosome number is maintained because each daughter cell receives one copy of every chromosome.
    • Mitosis separates the sister chromatids so that each new nucleus gets a complete set of chromosomes.
    • Cytokinesis divides the cytoplasm to form two separate daughter cells.
    • The two daughter cells are genetically identical to each other and to the original parent cell.

    Common mistakes and how to put them right

    • Saying the chromosome number doubles during interphase.

      Put it right by stating that the DNA amount doubles but the chromosome number stays the same because the copies remain attached as sister chromatids.

    • Thinking the daughter cells are genetically different.

      Put it right by stating that mitosis produces genetically identical cells because each receives the same chromosome copies.

    • Confusing DNA replication with protein synthesis.

      Put it right by stating that replication copies DNA, whereas protein synthesis uses DNA instructions to build proteins.

    Exam tips

    • Use the terms DNA replication, sister chromatids and genetically identical accurately in your answer.
    • State clearly that the chromosome number is maintained, not doubled, in the daughter cells.
    • Link the doubling of genetic material to interphase and the separation to mitosis when explaining the process.

    Try the lesson

    The start of the Mitosis and the cell cycle: During the cell cycle the genetic material is doubled and then divided into two identical cells. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What is produced at the end of the cell cycle when a body cell divides by mitosis?

    See it

    A top-to-bottom flowchart with eight boxes joined by arrows. The first box is the parent cell, which leads to a box saying that in interphase DNA replication doubles the genetic material. This leads to a box saying each chromosome is two identical sister chromatids joined at a centromere. Next, a box says mitosis separates the sister chromatids, leading to a box saying one copy of each chromosome goes into each new nucleus. This leads to a box saying cytokinesis divides the cytoplasm, then to a box saying two genetically identical daughter cells, and finally to a box saying the same chromosome number as the parent cell.
    It shows the sequence of the cell cycle from DNA replication in interphase, through mitosis and cytokinesis, to two genetically identical daughter cells with the same chromosome number as the parent.

    Put it in order

    Put these steps in the order they happen.

    1. 1. Interphase: DNA replication doubles the genetic material
    2. 2. Each chromosome is two identical sister chromatids joined at a centromere
    3. 3. Mitosis separates the sister chromatids
    4. 4. One copy of each chromosome goes into each new nucleus
    5. 5. Cytokinesis divides the cytoplasm
    6. 6. Two genetically identical daughter cells
    7. 7. Same chromosome number as the parent cell
    8. 8. Parent cell

    Key words

    Say what each word means before you turn the card.

    DNA replication

    Try answering aloud or in your head before turning the card.

    Sister chromatids

    Try answering aloud or in your head before turning the card.

    Mitosis

    Try answering aloud or in your head before turning the card.

    Cytokinesis

    Try answering aloud or in your head before turning the card.

    See every definition
    DNA replication
    During interphase, the genetic material is doubled, producing two identical copies of each chromosome.
    Sister chromatids
    Two identical copies of each chromosome, held together at a centromere.
    Mitosis
    The process in which the sister chromatids are separated so that one copy of each chromosome goes into each new nucleus.
    Cytokinesis
    The process that divides the cytoplasm, forming two separate daughter cells.

    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-to-bottom flowchart with eight boxes joined by arrows. The first box is the parent cell, which leads to a box saying that in interphase DNA replication doubles the genetic material. This leads to a box saying each chromosome is two identical sister chromatids joined at a centromere. Next, a box says mitosis separates the sister chromatids, leading to a box saying one copy of each chromosome goes into each new nucleus. This leads to a box saying cytokinesis divides the cytoplasm, then to a box saying two genetically identical daughter cells, and finally to a box saying the same chromosome number as the parent cell.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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