Gene Expression and Cancer: AQA A Level Biology Exam Questions by Topic

AQAGene Expression and CancerExam Questions
Written by Tom Whitburn

Gene expression and cancer (AQA 3.8.2.3) is A-level only, so it's Year 13 content. You need the main differences between benign and malignant tumours, how mutations and abnormal methylation of tumour suppressor genes and oncogenes lead to tumours, and how increased oestrogen concentrations cause some breast cancers. You also have to evaluate evidence linking genetic and environmental factors to cancer, and interpret how this knowledge is used to prevent and treat it.

The examiners' reports show where the marks go. Students write about uncontrolled cell 'growth' instead of cell division, say an oncogene makes 'no protein' when it makes more or altered protein, and mix up mutation with methylation: only 6% got full marks explaining how BRCA1 and BRCA2 mutations cause cancer. On data questions most assumed that more CAG repeats meant more prostate cancer, and fewer than 30% scored anything on that table of P values.

Start with tumour suppressor genes and oncogenes, then methylation and oestrogen, and finish with the data and evaluation questions, quoting numbers from each table or graph. If you'd like help with this topic, my AQA masterclasses run online on Tuesdays at 5.15pm for Year 12 and on Wednesdays or Thursdays at 6.30pm for Year 13.

Want help with this topic? It comes up in my weekly AQA masterclasses. See the timetable →

What you need from GCSE and Year 12

Each question on this page assumes you're secure on these GCSE and Year 12 ideas. If any of them feels shaky, revise it before you start.

  • GCSE: cancer is the result of changes in cells that lead to uncontrolled growth and division, forming a benign or malignant tumour.
  • Year 12 (AQA 3.2.2): cells divide by mitosis in the cell cycle, and uncontrolled cell division can lead to tumours.
  • Year 12 (AQA 3.1.4.2): a competitive inhibitor has a similar shape to the substrate and binds to the enzyme's active site.
  • Year 13 (AQA 3.8.1): a gene mutation changes the base sequence of DNA and can change the amino acid sequence and tertiary structure of a protein.
  • Year 13 (AQA 3.8.2.2): transcription factors bind to the promoter so RNA polymerase can start transcription, and increased methylation of DNA inhibits transcription.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Benign tumour: a tumour that grows slowly, is usually surrounded by a capsule and doesn't spread to other parts of the body.
  • Malignant tumour: a cancer: a tumour that grows rapidly, invades nearby tissue and can spread (metastasise) to other parts of the body.
  • Tumour suppressor gene: a gene whose protein slows or stops cell division, for example until damaged DNA is repaired; if it is mutated or not transcribed, cell division becomes uncontrolled.
  • Oncogene: a mutated form of a gene that stimulates cell division; it makes more of, or an altered, protein, so division is rapid and uncontrolled.
  • Abnormal methylation: increased methylation (hypermethylation) of a tumour suppressor gene stops it being transcribed; decreased methylation of an oncogene can switch it on.
  • DNA methyltransferase: an enzyme that adds methyl groups to cytosine bases in DNA.
  • Oestrogen: a steroid hormone that binds to a receptor and activates a transcription factor; increased concentrations can cause some breast cancers.
  • ER-positive breast cancer: a breast cancer whose cells have oestrogen receptors, so it develops when oestrogen concentrations increase.
  • Rapid or uncontrollable cell division: the mark-scheme phrase for how a tumour forms; 'growth' on its own is ignored.
  • P value: the probability that a difference or association is due to chance; below 0.05 it is significant.

What these questions cover (AQA 3.8.2.3)

The questions test these statements from the AQA AS and A-level Biology specification (7401/7402):

  • Benign and malignant tumours: The main characteristics of benign and malignant tumours. (no written question asks you to compare benign and malignant tumours; the tumour cell calculation is the only part here, so learn the differences (growth rate, capsule, metastasis) from your notes)
  • Tumour suppressor genes and oncogenes: tumour suppressor genes and oncogenes
  • Abnormal methylation: abnormal methylation of tumour suppressor genes and oncogenes
  • Oestrogen and breast cancer: increased oestrogen concentrations in the development of some breast cancers.
  • Evaluating evidence on cancer: evaluate evidence showing correlations between genetic and environmental factors and various forms of cancer
  • Using oncogenes and tumour suppressor genes in treatment: interpret information relating to the way in which an understanding of the roles of oncogenes and tumour suppressor genes could be used in the prevention, treatment and cure of cancer.

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 14 questions are worth 42 marks, so about 55 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Tumour suppressor genes and oncogenes (3.8.2.3)

Question 1

A level Paper 2 · June 2018 · Q02.2 · 3 marks · Easy

Describe how alterations to tumour suppressor genes can lead to tumours.

Question text: describe how alterations to tumour suppressor genes can lead to the development of tumours, 3 marks.
Show the mark scheme Mark scheme, any three: (increased) methylation of tumour suppressor genes; mutation in tumour suppressor genes; the genes are not transcribed or expressed, or the amino acid sequence or primary structure is altered; results in rapid or uncontrollable cell division. Ignore growth.

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From the examiners' report: One in three got full marks. Give both alterations, mutation and methylation, say what each does (altered primary structure, or no transcription), and finish with uncontrolled cell division. Oncogenes aren't asked for.

Question 2

A level Paper 2 · June 2022 · Q10.1 · 3 marks · Medium

Explain how mutations in BRCA1 and BRCA2 can cause cancer.

Passage: BRCA1 and BRCA2 code for tumour suppressor proteins, and inherited mutations increase the risk of breast and ovarian cancers; ER-positive breast cancers have oestrogen receptors and develop with increased oestrogen; high PSA in blood can indicate prostate cancer but also urinary infections or an enlarged prostate; several cancers result from epigenetic abnormalities. Question: mutations in BRCA1 and BRCA2 can cause cancer (lines 1–2); explain how, 3 marks.
Show the mark scheme Mark scheme: change in DNA base sequence or triplet; change in sequence of amino acids, or primary or tertiary structure; results in rapid or uncontrollable cell division. Ignore growth; reject different amino acids formed.

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From the examiners' report: Only 6% got all three. Say the DNA base sequence changes, then the amino acid sequence and tertiary structure of the protein, then uncontrolled cell division. Don't confuse mutation with methylation.

Question 3

A level Paper 2 · June 2023 · Q08.1 · 3 marks · Medium

Explain how an alteration in the KRAS gene can cause a tumour.

Question text: the KRAS gene codes for K-Ras, a protein that relays signals from outside a cell to the nucleus, stimulating cell division; an alteration in KRAS produces an oncogene that can cause a tumour. Question asks you to suggest and explain how an alteration in the KRAS gene can cause a tumour to develop, 3 marks.
Show the mark scheme Mark scheme: mutation or change in base sequence of KRAS (accept in the promoter); change in the signalling protein or more K-Ras produced; results in rapid or uncontrollable cell division. Reject no protein or a non-functional protein; ignore epigenetic modifications.

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From the examiners' report: About 15% got all three. An oncogene makes more K-Ras, or an altered K-Ras, that keeps stimulating division; it doesn't make 'no protein'. Say mutation, not 'alteration'.

Question 4

A level Paper 3 · June 2017 · Q05.4 · 3 marks · Easy

Predict the effects of a non-functional form of the DNA repair enzyme ATM.

Question text: a mutagenic agent can break DNA; the enzyme ATM binds to the broken DNA, which activates a protein coded for by a tumour suppressor gene and stops cell division until the DNA is repaired. A mutation could give a person non-functional forms of the ATM gene. Question asks what you can predict about the possible effects, 3 marks.
Show the mark scheme Mark scheme, any three: ATM won't bind to broken DNA; DNA not repaired; cell division continues or a tumour forms; tumour suppressor gene not activated; may have no effect in a heterozygous organism that still has a functional ATM gene.

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From the examiners' report: 47% got all three. Follow the chain in the stem step by step: no binding, no activation of the tumour suppressor protein, so cells with broken DNA keep dividing and a tumour can form.

Abnormal methylation and oestrogen (3.8.2.3)

Question 5

A level Paper 3 · November 2020 · Q05.2 · 3 marks · Medium

Suggest how EGCG from green tea lets throat cancer cells make mRNA from a tumour suppressor gene.

Stem: increased methylation of the promoter region of a tumour suppressor gene causes one type of throat cancer, and the methylation, caused by the enzyme DNMT, passes to daughter cells. EGCG, a chemical in green tea, is a competitive inhibitor of DNMT and lets daughter cells produce mRNA from the tumour suppressor gene. Question: suggest how EGCG allows the production of mRNA in daughter cells, 3 marks.
Show the mark scheme Mark scheme, any three: EGCG binds to the active site of DNMT; DNMT can't methylate the promoter region; transcription factors can bind to the promoter; RNA polymerase is stimulated or activated.

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From the examiners' report: Only 14% got all three. EGCG is the inhibitor and DNMT is the enzyme: EGCG fills DNMT's active site, so the promoter isn't methylated and transcription factors can bind. It doesn't bind to the promoter.

Question 6

A level Paper 2 · November 2021 · Q06.2 · 3 marks · Medium

Suggest how the DNA methyltransferase inhibitor AZA reduces the effects of MDS.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Stem: myelodysplastic syndromes (MDS) are malignant cancers in which the bone marrow doesn't produce healthy blood cells. Question text: MDS can develop from epigenetic changes to tumour suppressor genes; the drug AZA inhibits DNA methyltransferases, enzymes that add methyl groups to cytosine bases. Question asks you to suggest and explain how AZA can reduce the effects of MDS in some patients, 3 marks.
Show the mark scheme Mark scheme: AZA reduces methylation of DNA or the gene; the tumour suppressor gene is transcribed or expressed; prevents rapid or uncontrollable cell division. Reject any reference to mutation; ignore 'switched on'.

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From the examiners' report: 42% got two or more marks. Say the tumour suppressor gene is transcribed, not 'switched on' or 'translated', and then link its protein to controlling cell division.

Question 7

A level Paper 2 · November 2021 · Q06.4 · 2 marks · Easy

Read a survival graph to find how many more patients survived 10 months on AZA.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Context: 360 patients with MDS were randomised 1:1 to receive AZA or conventional drugs. Figure 6: proportion surviving (0.4 to 1.0) against time after treatment (0 to 15 months); at 10 months about 0.74 for AZA and 0.58 for conventional drugs. Question: use Figure 6 and the information to calculate the difference in the number of patients surviving at 10 months, 2 marks.
Show the mark scheme Mark scheme: 29 or 28.8 = 2 marks; 1 mark for 0.74 and 0.58, for 58 or 57.6, or for 28.

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From the examiners' report: About 34% got both marks. Each group had 180 patients: (0.74 − 0.58) × 180 = 28.8, so 29 patients. Rounding 28.8 down to 28 lost a mark.

Question 8

A level Paper 2 · June 2022 · Q10.3 · 3 marks · Medium

Explain how drugs with a similar structure to oestrogen treat ER-positive breast cancer.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Passage as before: ER-positive breast cancers have receptors for oestrogen and develop as a result of increased oestrogen concentrations in the blood. Question: effective treatment often uses drugs with a similar structure to oestrogen (lines 9–10); suggest and explain how these drugs are an effective treatment, 3 marks.
Show the mark scheme Mark scheme: the drug binds to the oestrogen (ER) receptor or transcription factor; prevents oestrogen binding; no or fewer transcription factors bind to the promoter, or RNA polymerase isn't stimulated. Reject active site or enzyme-substrate complex.

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From the examiners' report: Only 7% got all three, though 75% got one. The drug binds to the oestrogen receptor so oestrogen can't; then say the transcription factor doesn't bind to the promoter, so genes for cell division aren't transcribed.

Evaluating evidence about cancer (3.8.2.3)

Question 9

A level Paper 2 · June 2018 · Q02.3 · 2 marks · Easy

Calculate how many malignant tumour cells there are after 4 weeks of division every 8 hours.

Question text: a type of malignant tumour cell divides every 8 hours; starting with one cell and assuming none die, how many tumour cells will be present after 4 weeks? Give your answer in standard form, 2 marks.
Show the mark scheme Mark scheme: 1.9 or 1.93 × 10²⁵ (accept 2 × 10²⁵) = 2 marks; 1 mark for showing 84 divisions, 28 × 3, or 672 ÷ 8.

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From the examiners' report: Over 83% got a mark, almost always for 84 divisions, and about half went on to the right answer. The number of cells is 2⁸⁴, not 84² or 28³.

Question 10

A level Paper 2 · June 2022 · Q10.4 · 2 marks · Medium

Explain why a blood test for PSA may not be conclusive for prostate cancer.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Passage as before: men with prostate cancer have a high concentration of prostate-specific antigen (PSA) in their blood, but urinary infections and a naturally enlarged prostate can also increase PSA concentrations (line 11). Question: explain why blood test results may not be conclusive when testing for prostate cancer, 2 marks.
Show the mark scheme Mark scheme: high PSA isn't always linked to prostate cancer, or could be a false positive; could be due to a urinary infection or an enlarged prostate.

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From the examiners' report: 49% got both marks from the passage. Say a high PSA concentration could be a false positive, then give the other cause from the passage: a urinary infection or an enlarged prostate, not just 'infection'.

Question 11

A level Paper 2 · June 2023 · Q08.2 · 5 marks · Medium

Draw conclusions about type II diabetes, metformin and survival of colorectal cancer patients.

Question text: alterations in KRAS can cause colorectal cancer (CRC); scientists compared survival of CRC patients with type II diabetes given no drug (A), metformin (B) or a combination including metformin (C) with patients with no history of diabetes. Table 1: mean survival time in months and P values: no diabetes 32.2; A 21.3, P = 0.007; B 49.7, P = 0.022; C 38.3, P = 0.636. Question: what can you conclude about the effects of type II diabetes and the drug treatments on survival time? 5 marks.
Show the mark scheme Mark scheme, any five: A (untreated) has the lowest survival; B (metformin) has the highest; C increases survival; A and B differ significantly from the control; C doesn't differ significantly; other drugs reduced the effect of metformin, or metformin alone is more effective. Ignore sample size or repeats.

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From the examiners' report: About 9% got all five. Most used the survival times; fewer used the P values. Say A and B differ significantly from the control (P < 0.05) and C doesn't. A higher P value doesn't mean more significant.

Question 12

A level Paper 2 · June 2025 · Q08.4 · 4 marks · Medium

Evaluate a conclusion linking the number of VNTR repeats to breast cancer risk.

Question text: scientists determined the risk of breast cancer in women with 2, 3 or 4 repeats of one VNTR and without it, and calculated the odds ratio (risk with the VNTR : risk without). Table 5: 2 repeats 0.55 : 1; 3 repeats 1.58 : 1; 4 repeats 1.94 : 1. Question: a student concluded that the number of repeats is associated with the risk of breast cancer; evaluate this conclusion, 4 marks.
Show the mark scheme Mark scheme (mark points 1 and 2 needed for full marks): two repeats decreases risk; three and four repeats increase risk; no results for more than 4 or for 1 repeat; other factors such as age affect risk; breast cancers aren't all the same type; sample size not known.

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From the examiners' report: Fewer than 10% got all four. An odds ratio below 1 means lower risk, so two repeats reduce risk and three or four increase it. Then give limits: few repeat numbers, other risk factors, sample size unknown.

Question 13

A level Paper 2 · November 2020 · Q02.4 · 3 marks · Hard

Conclude what a table of P values shows about CAG repeats and prostate cancer.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Stem: testosterone is a steroid hormone; the gene for the androgen receptor (AR) has a variable number of CAG repeats, and some studies link the number to prostate cancer risk. Table 1: number of CAG repeats in the AR gene and P value: ≤16, 0.02; ≤17, 0.30; ≤18, 0.07; ≤19, 0.09; ≥20, 0.06. Question: what can you conclude from the data in Table 1? 3 marks.
Show the mark scheme Mark scheme, any three: with 16 or fewer repeats the association is significant; with 17 or more it isn't; explanation of the P value (less than 0.05 or 5% probability of being due to chance, or e.g. 0.30 is a 30% probability); reject the null hypothesis at 16 or fewer, accept it at 17 or more.

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From the examiners' report: Fewer than 30% scored and only 6% got all three. The table shows P values, not risk: only ≤16 repeats (P = 0.02) is below 0.05, so only that association is significant.

Question 14

A level Paper 3 · November 2020 · Q05.3 · 3 marks · Medium

Give reasons why green tea may not be a cure for cancer.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Stem as before: increased methylation of a tumour suppressor gene promoter causes one type of throat cancer, and EGCG from green tea inhibits DNMT. Figure 2: rate of growth of throat cancer cells in vitro as a percentage of maximum against EGCG (0, 5, 10, 20 and 50 µmol): about 100, 96, 97, 64 and 48%, with 20 and 50 µmol marked as a significant effect. Question: a reporter concluded that drinking green tea could be a cure for cancer; suggest three reasons why this might not be valid, 3 marks.
Show the mark scheme Mark scheme, any three: only throat cancer investigated; not all cancers are caused by methylation; only a significant reduction at 20 or 50 µmol; don't know how much EGCG is in green tea; it only reduces growth rate, with no evidence of a cure; cells in the body might respond differently from those in vitro.

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From the examiners' report: Only 11% scored zero, but many lost marks to rote answers such as 'no statistical test' or 'no control' when Figure 2 shows both. Use the study itself: one cancer, cells in vitro, and growth slowed rather than cured.

Where students lose marks (from AQA examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Tumours come from cell division, not 'growth': On BRCA1 and BRCA2 almost 80% got the cell division mark, but those who didn't usually wrote about the growth of cells. A significant minority did the same when describing tumour suppressor genes.

    ✔ Gains credit: "(Results in) rapid/uncontrollable cell division" (mark schemes say "ignore growth").

  • A mutation changes the DNA bases; methylation doesn't: Only 6% got all three marks for BRCA1 and BRCA2. Very few explained what a mutation is, some wrote about the 'amino acid sequence of a gene', and a surprisingly large number confused mutation with methylation.

    ✔ Gains credit: "Change in DNA base sequence/triplet"; "change in (sequence of) amino acids OR change in primary/tertiary structure".

  • An oncogene makes more or altered protein, not none: About 15% got all three marks for KRAS. Many said no protein or a non-functional protein was made, gave epigenetic changes instead of a mutation, or just repeated 'an alteration in the gene'.

    ✔ Gains credit: "Mutation (in KRAS gene)"; "change in (signalling) protein OR more (signalling) protein/K-Ras produced".

  • Less methylation means the gene is transcribed again: 42% got at least two marks for AZA. Most said it reduces methylation but fewer said the tumour suppressor gene is transcribed, using 'switched on' or even 'translated' instead.

    ✔ Gains credit: "(AZA) reduces methylation"; "(tumour suppressor) gene is transcribed/expressed"; "cell division can be controlled".

  • EGCG binds DNMT, not the promoter: Only 14% got all three marks. Students mixed up the enzyme and the substrate and said EGCG binds to the promoter, though the stem says it's a competitive inhibitor of DNMT.

    ✔ Gains credit: "(EGCG) binds to active site of DNMT"; "(DNMT) cannot methylate (promoter region)"; "transcription factor(s) can bind (to promoter region)".

  • Oestrogen-like drugs block the receptor: Only 7% got all three marks for ER-positive breast cancer drugs. Some said 'competitive inhibitor' without binding, talked about active sites, or said the drug binds to oestrogen; only the best mentioned the promoter or RNA polymerase.

    ✔ Gains credit: "(Drug) binds to (oestrogen/ER) receptor"; "prevents binding of oestrogen"; "no/fewer transcription factor(s) bind to promoter OR RNA polymerase not stimulated".

  • Only 16 repeats or fewer was significant: Fewer than 30% scored on the CAG repeats table and only 6% got all three. Most concluded that more repeats meant more prostate cancer, and many read the P values as the chance of getting cancer.

    ✔ Gains credit: "With 16 or fewer (repeats the association) is significant"; "with 17 or more (repeats the association) is not significant"; "less than a 5% probability of being due to chance".

  • Two repeats lowered the risk; read every odds ratio: Fewer than 10% got all four marks on the VNTR odds ratios. Most said more repeats always increased the risk, which was ignored; you needed both directions to reach full marks.

    ✔ Gains credit: "Two repeats decreases (risk of) breast cancer"; "three and four repeats increases (risk of) breast cancer"; "no results for more than 4 repeats".

Download the questions

Download the PDF pack (14 questions, mark schemes at the end)

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Questions, mark schemes and examiners' report extracts © AQA.

Tom Whitburn
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