Explain why the daughter cells produced by mitosis must be genetically identical to the parent cell, and describe the role of the cell cycle in ensuring this outcome.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In the human body, millions of cells are produced every second to replace worn-out or damaged tissue. These new cells are produced by mitosis.
Model answer (4 marks)
Mitosis must give genetically identical daughter cells because the parent cell’s DNA is first copied during interphase. The two identical chromatids are then separated during mitosis so that each new cell receives a complete set of chromosomes.
The cell cycle guarantees this. In G1 the cell grows and checks conditions, in S it replicates its DNA, and in G2 it prepares for division. Only after this sequence can the cell enter mitosis, ensuring that every division starts with a fully replicated genome and that the resulting daughter cells are diploid and genetically identical to the parent.
The cell cycle guarantees this. In G1 the cell grows and checks conditions, in S it replicates its DNA, and in G2 it prepares for division. Only after this sequence can the cell enter mitosis, ensuring that every division starts with a fully replicated genome and that the resulting daughter cells are diploid and genetically identical to the parent.
Examiner tips
- Mention DNA replication in interphase and chromosome separation in mitosis; link to diploidy; include the G1–S–G2 sequence of the cell cycle.
- Use precise terms: interphase, S phase, chromatids, diploid, genetically identical.
- Keep answer concise – 4 marks allow a short paragraph, not a long essay.
Common mistakes
- Confusing meiosis with mitosis; describing gamete formation.
- Omitting the role of the S phase or the cell cycle stages.
- Using vague language such as "the same genes" instead of "identical DNA".
Mark scheme (4 marks)
- Mitosis produces daughter cells that are genetically identical because DNA replication occurs (during interphase) so each daughter cell receives the same genetic information as the parent cell.
- During mitosis, the replicated chromosomes (chromatids) are separated and pulled to opposite poles of the cell, so each new cell receives a full set of chromosomes.
- The daughter cells produced are diploid, containing two copies of each chromosome, the same number as the parent cell.
- The cell cycle ensures this process is repeated, including a growth phase and DNA replication (interphase) before every division, so every new cell produced has the correct genetic information.
Key terms in this question
mitosis · cell cycle · daughter cells
Related
- Revision notes: Mitosis and the cell cycle →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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