Genetic Diversity and Adaptation: AQA A Level Biology Exam Questions by Topic

AQAGenetic Diversity and AdaptationExam Questions
Written by Tom Whitburn

Genetic diversity and adaptation (AQA 3.4.4) is where natural selection gets the A-level treatment. You need to know genetic diversity as the number of different alleles in a population, explain how a random mutation produces a new allele that can increase reproductive success, and show how that allele is passed on and rises in frequency over many generations. You also need directional selection, with antibiotic resistance in bacteria as the example, and stabilising selection, with human birth weights, and you need to apply all of this to data and contexts you've never seen before.

The examiners' reports keep finding the same problems. Students write 'gene' when they mean 'allele', say antibiotics cause mutations or that bacteria become immune, give stock answers that never mention the organism in the question, invent types of selection that aren't in the specification, and say the number of alleles goes up rather than the frequency.

Start with the core natural selection explanations, then the antibiotic resistance questions, and finish with the data and evaluation questions on fish, birth weights, guppies and bacteria. Answer each question on paper before you open the mark scheme. 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.

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: variation within a species can be genetic, environmental or both, and new variants arise from random mutations in DNA.
  • GCSE: in evolution by natural selection, individuals with characteristics best suited to their environment are more likely to survive and breed, passing on their genes.
  • GCSE: antibiotic-resistant bacteria such as MRSA arise by mutation, and they spread because the antibiotic kills the non-resistant bacteria.
  • Year 12 (AQA 3.4.3): a gene mutation is a change in the base sequence of DNA, and mutations arise spontaneously during DNA replication.
  • Year 12 (AQA 3.2.2): prokaryotic cells divide by binary fission, so a resistance allele is passed to both daughter cells.

Key terms

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

  • Genetic diversity: the number of different alleles of genes in a population.
  • Allele: a different form of a gene; mark schemes reject 'gene' when 'allele' is meant.
  • Mutation: a random change in the base sequence of DNA that can result in a new allele of a gene; it isn't caused by the selection pressure.
  • Selection pressure: an environmental factor, such as an antibiotic or a predator, that makes individuals with one allele more likely to survive and reproduce than others.
  • Reproductive success: surviving to reproduce and passing an advantageous allele on to the next generation.
  • Allele frequency: the proportion (or percentage) of a population's alleles of a gene that are one particular allele; examiners don't accept 'number' for frequency.
  • Directional selection: selection that favours one extreme of the range of a characteristic, such as antibiotic resistance in bacteria.
  • Stabilising selection: selection against both extremes, favouring the middle of the range, such as human birth weights.
  • Antibiotic resistance: bacteria with a resistance allele survive the antibiotic and reproduce; it is not immunity.
  • Adaptation: an anatomical, physiological or behavioural feature that makes an organism better adapted to its environment, produced by natural selection.

What these questions cover (AQA 3.4.4)

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

  • Genetic diversity: Genetic diversity as the number of different alleles of genes in a population. (none of the written questions available asks for this definition on its own)
  • Genetic diversity and natural selection: Genetic diversity is a factor enabling natural selection to occur. (none of the written questions available tests this on its own, but every selection question here relies on it)
  • Natural selection: The principles of natural selection in the evolution of populations.
  • New alleles: Random mutation can result in new alleles of a gene.
  • Advantageous alleles: Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.
  • Inheritance: The advantageous allele is inherited by members of the next generation.
  • Allele frequency: As a result, over many generations, the new allele increases in frequency in the population.
  • Types of selection: Directional selection, exemplified by antibiotic resistance in bacteria, and stabilising selection, exemplified by human birth weights.
  • Adaptation: Natural selection results in species that are better adapted to their environment. These adaptations may be anatomical, physiological or behavioural. (none of the written questions available asks about anatomical, physiological or behavioural adaptations; the AMY1 question treats extra gene copies as an adaptation to diet)
  • Selection in unfamiliar contexts: use unfamiliar information to explain how selection produces changes within a population of a species
  • Interpreting selection data: interpret data relating to the effect of selection in producing change within populations
  • Adaptation, selection and evolution: show understanding that adaptation and selection are major factors in evolution and contribute to the diversity of living organisms. (none of the written questions available tests this statement on its own)

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 18 questions are worth 52 marks, so about 68 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.

Mutation, natural selection and allele frequency (3.4.4)

Question 1

AS Paper 2 · June 2023 · Q06.3 · 4 marks · Medium

Describe how natural selection may have led to all mammals in a population producing the enzyme CEL.

Question text: mammals feed their young on milk and CEL digests the triglycerides in milk; the ability to produce CEL occurred due to a gene mutation; describe how natural selection may have led to all mammals in a population producing CEL, 4 marks.
Show the mark scheme Mark scheme, max 4: mutation results in a new allele; those with the allele can digest milk or triglycerides; individuals with the allele are more likely to survive and reproduce; directional selection; increase in frequency of the allele in the population.

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From the examiners' report: Only around 20% got 3 or more. Write 'allele', not 'gene', and don't just repeat the stem. Name directional selection and say the allele's frequency increases.

Question 2

A level Paper 2 · June 2018 · Q09.1 · 4 marks · Hard

Describe how farming cattle for milk could have led to an increase in lactase persistence in humans.

Passage: lactose in milk is hydrolysed by lactase; some humans keep producing lactase as adults (lactase persistence, LP), controlled by a dominant allele. Question asks how farming cattle as a source of milk could have led to an increase in LP, 4 marks.
Show the mark scheme Mark scheme, max 4: LP allele due to mutation; milk provides a named nutrient such as glucose, galactose or protein; individuals with LP more likely to survive and reproduce; directional selection; frequency of the allele increases in the next generation. Reject mutation caused by drinking milk, and 'LP gene'.

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From the examiners' report: Fewer than 13% got more than 2. The mutation isn't caused by drinking milk; name a nutrient, not 'sugar'; write allele, not gene. LP is in the humans, not the cattle.

Question 3

AS Paper 2 · June 2017 · Q03.3 · 3 marks

Suggest how multiple copies of the amylase gene AMY1 evolved through natural selection as an adaptation to a high-starch diet.

Question text: multiple copies of the AMY1 gene is an adaptation to a high-starch diet; suggest how this evolved through natural selection, 3 marks.
Show the mark scheme Mark scheme: mutations produce extra copies of the AMY1 gene; those with more copies survive or reproduce better on a high-starch diet; and pass on the multiple copies to their offspring.

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From the examiners' report: No examiners' report for this part. The mark scheme wants three steps: a mutation gives the extra copies, people with them do better on a high-starch diet, and they pass the copies on.

Question 4

A level Paper 1 · June 2023 · Q03.5 · 4 marks · Medium

Use natural selection to explain why resistance to P. vivax malaria is so common in Africa.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 3: phylogenetic diagram of strains of P. vivax evolving from an African common ancestor and spreading to Europe, Asia and the Americas. Question: most of the human population in Africa are resistant to P. vivax malaria; explain why, using natural selection, 4 marks.
Show the mark scheme Mark scheme: mutation produced an allele; those with the allele or resistance are less likely to get malaria, or survive it; so are more likely to reproduce and pass on the allele; over generations the allele frequency increases. Reject mutation caused by infection.

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From the examiners' report: 40% got 3 or 4. Stock phrases with no mutation or malaria miss the first two marks. Say a mutation produced an allele in humans, not in P. vivax, and write resistance, not immunity.

Question 5

AS Paper 2 · November 2021 · Q06.3 · 4 marks

Suggest and explain why the frequency of the ADF allele in fruit flies fed alcohol changed over 45 generations.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Earlier part of the same exam question, giving the information this part uses. Passage: fruit flies have a gene for alcohol dehydrogenase (AD) with alleles ADF and ADS; a scientist fed 100 flies food containing alcohol and let them reproduce for 45 generations. Table 2: frequency of ADF was 0.20 at generation 0 and 0.74 at generation 45.
Show the mark scheme Mark scheme: flies with ADF have a selective advantage in the presence of alcohol; so are more likely to reproduce; and pass on the ADF allele; so the allele frequency increases. Accept the converse for ADS.

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From the examiners' report: No examiners' report for this paper. The mark scheme wants a chain: selective advantage with alcohol, more likely to reproduce, pass on ADF, so its frequency increases.

Directional selection and antibiotic resistance (3.4.4)

Question 6

AS Paper 1 · June 2025 · Q09.1 · 1 mark · Medium

Name the type of natural selection by which penicillin-resistant S. aureus evolved.

Passage: penicillin was used extensively from 1941 and by the late 1960s over 80% of S. aureus were resistant; resistant bacteria have a blaZ allele coding for beta lactamase, which hydrolyses penicillin; MRSA appeared by 1961. Question: name the type of natural selection, 1 mark.
Show the mark scheme Mark scheme: directional.

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From the examiners' report: Slightly under 50% wrote directional. 'Mutation', 'survival of the fittest' and 'adaptations' aren't types of selection.

Question 7

AS Paper 1 · June 2025 · Q09.2 · 3 marks · Hard

Explain why more than 80% of S. aureus were resistant to penicillin by the late 1960s.

Question text: by the late 1960s, more than 80% of S. aureus were resistant to penicillin (lines 3 to 4 of the passage); explain why, 3 marks.
Show the mark scheme Mark scheme: penicillin creates a selection pressure, or kills non-resistant bacteria; resistant bacteria are more likely to survive and reproduce to pass on the blaZ, penicillin-resistance or beta lactamase allele; increased frequency of the blaZ allele in the next generation. Reject 'gene' for 'allele' once.

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From the examiners' report: About 5% got all 3. Bacteria are resistant, not 'immune'. Name the blaZ or penicillin-resistance allele, not just a 'beneficial allele', and say its frequency increases.

Question 8

A level Paper 1 · June 2022 · Q02.1 · 3 marks · Medium

Explain how antibiotic use has made resistant C. difficile a common cause of infection acquired in hospital.

Question text: Clostridium difficile causes disease in humans and antibiotic-resistant strains are a common cause of infection acquired in hospital; explain how the use of antibiotics has led to this, 3 marks.
Show the mark scheme Mark scheme: some bacteria have alleles for resistance; antibiotics are the selection pressure, or non-resistant bacteria die, or resistant bacteria survive and reproduce; more antibiotics used in hospital, or patients have weakened immune systems, or high frequency of the resistance allele. Reject antibiotics causing the resistance allele.

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From the examiners' report: 80% scored at least 1. Antibiotics don't cause mutations, and bacteria don't make an immune response. For the hospital mark, say more antibiotics are used there or patients have weakened immune systems.

Question 9

AS Paper 2 · June 2018 · Q08.4 · 2 marks · Hard

Suggest and explain why tetracycline-resistant bacteria are more common than streptomycin-resistant bacteria in farm animals.

Table 5: percentage of antibiotic-resistant bacteria in the intestines of farm animals given antibiotics in their food: tetracycline 29%, streptomycin 13%. Question asks for one reason why tetracycline-resistant bacteria are more common, 2 marks.
Show the mark scheme Mark scheme, one pair: tetracycline used more often or in higher doses, so resistant bacteria more likely to survive, reproduce and pass on the resistance allele; or more mutations for tetracycline resistance, so passed on to more bacteria; or tetracycline used for longer, giving more time for mutation or selection. Reject mutation caused by the antibiotic.

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From the examiners' report: Most got 1 mark for more tetracycline or longer use. Then explain: resistant bacteria survive, reproduce and pass on the resistance allele. Antibiotics don't cause mutations.

Question 10

AS Paper 2 · June 2018 · Q08.5 · 1 mark · Hard

Suggest why tetracycline resistance stayed constant after farm animals stopped being given tetracycline.

Question text: in recent years these farm animals have not been given tetracycline in their food, but the percentage of bacteria resistant to tetracycline has remained constant; suggest one reason why, 1 mark.
Show the mark scheme Mark scheme, one of: no selection against resistant bacteria; bacteria pass on the resistance allele when they reproduce; resistant bacteria passed from one generation of animals to the next; environment doesn't change, so stabilising selection. Reject mitosis or immunity.

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From the examiners' report: Only 16.7% scored. With no selection against them, resistant bacteria still pass on the resistance allele when they reproduce. The animals' immune response isn't relevant.

Question 11

A level Paper 1 · June 2017 · Q05.5 · 3 marks

Explain why patients with a bladder infection should be treated with both the current and the new antibiotic.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Earlier part of the same exam question, giving the information this part uses. Figure 2: bar chart of log10 number of bacteria in the bladder of mice: about 4.8 in untreated group C, 2.8 in group R given the current antibiotic and 1.2 in group A given the new antibiotic. Question asks why both antibiotics should be used together, 3 marks.
Show the mark scheme Mark scheme: from Figure 2, neither antibiotic kills all the bacteria, or some are resistant; resistant bacteria reproduce to produce more resistant bacteria; one antibiotic will kill bacteria resistant to the other, or bacteria are unlikely to be resistant to both. 'Use of both will be more effective' is insufficient.

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From the examiners' report: No examiners' report for this part. Use Figure 2: some bacteria survive each antibiotic. 'More effective' isn't enough: say one kills the bacteria resistant to the other.

Selection in unfamiliar contexts and data (3.4.4)

Question 12

AS Paper 2 · June 2019 · Q07.1 · 2 marks · Hard

Name the type of selection modelled by putting back only the largest or only the smallest fish, and give a reason.

Figure 8: mean mass of removed fish in grams over 4 years; Tank A (only largest fish put back) rises from about 3.1 to 4.8 g, Tank B (random) fluctuates around 3.5 to 3.9 g, and Tank C (only smallest put back) falls from about 3.4 to 2.4 g.
Show the mark scheme Mark scheme: directional; one extreme selected, removed, favoured or allowed to breed. Accept large or small fish for 'extreme'.

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From the examiners' report: Many named types of selection not in the specification, such as artificial, planned or continuous. Write directional, then say one extreme is favoured; 'to get the best fish' doesn't score.

Question 13

AS Paper 2 · June 2019 · Q07.4 · 3 marks · Medium

Evaluate whether the fish tank investigation supports using nets that let small fish escape in sea fishing.

Question text: sea fishing nets have a mesh size that lets small fish escape and captures large fish, to protect wild fish populations; using all the information in the question, evaluate whether the scientists' fish tank investigation supports these nets, 3 marks.
Show the mark scheme Mark scheme, max 3: not supported, because fishing reduces mean mass of fish, as large fish are removed, like Tank C; but, max 2: only one species; no statistical test; tank size may affect growth; fish all the same age; no measure of number, yield or reproductive success; removing 90% unlikely at sea; sea fish don't have a one-year life cycle.

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From the examiners' report: Just under half concluded it isn't supported, and about 1% gave both sides. State your conclusion clearly, and read the y-axis: it shows mean mass, not population size.

Question 14

A level Paper 1 · June 2019 · Q04.1 · 3 marks

Use a graph of 800 000 births to explain how human mass at birth is affected by stabilising selection.

Figure 5: population frequency against mass at birth from 0 to 7000 g; a bell-shaped curve for mass at birth peaks at about 3400 g, and a dashed U-shaped curve for transfer to a special care unit is high below about 2500 g and above about 4500 g.
Show the mark scheme Mark scheme: babies most likely to be transferred to special care are under 2800 g or over 4200 g; extreme mass babies least likely to survive to reproduce, so less likely to pass on their alleles; alleles for extreme mass decrease in frequency. Do not accept 'number' for 'frequency'.

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From the examiners' report: No examiners' report for this paper. Quote Figure 5, link survival to passing on alleles, and say alleles for extreme mass fall in frequency (or proportion), not number.

Question 15

AS Paper 2 · June 2022 · Q08.3 · 4 marks · Hard

Name the selection caused by adding predators to a guppy tank and explain how it changed allele frequency.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 9: mean number of spots per guppy rises over the generations. Figure 10: in a second tank, the mean number of spots rises until predators are added at the fourth generation, then falls.
Show the mark scheme Mark scheme: directional; fish with more spots are more likely to be predated; alleles for more spots not passed on; so the frequency of alleles for more spots decreases. Reject 'gene' once; ignore 'number of alleles decreases'.

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From the examiners' report: Under 4% got all 4, though over half got 1. Name directional selection and say which allele: fish with more spots are eaten, so alleles for more spots fall in frequency.

Question 16

A level Paper 1 · June 2018 · Q06.4 · 3 marks

Use directional selection to explain how breeding red clover increased the number of plants producing 2n gametes.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Earlier part of the same exam question, giving the information this part uses. Figure 6: a faulty meiosis that gives diploid (2n) gametes. Table 3: observed numbers of red clover plants that did not or did produce 2n gametes over breeding cycles 0 to 3: 50 and 4, then 14 and 42, then 2 and 44, then 0 and 56.
Show the mark scheme Mark scheme: the scientists selected plants that produced 2n gametes for breeding; so these plants passed on their alleles for 2n gametes; the frequency of these alleles increased. Do not accept 'number' for frequency.

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From the examiners' report: Many just described directional selection or said the environment changed. Use the stem: the scientists bred only from 2n plants, so their alleles were passed on and rose in frequency.

Question 17

AS Paper 2 · June 2016 · Q07.3 · 2 marks · Hard

Suggest why the high frequency of the CCR5 mutation in Europe is not due to natural selection by HIV.

Question text: the frequency of the CCR5 mutation, which gives a non-functional HIV receptor on helper T cells, is highest in Europe; scientists concluded from HIV data that this is not due to natural selection in response to HIV; suggest two reasons, 2 marks.
Show the mark scheme Mark scheme, any two: lower exposure to HIV, or fewer HIV infections, in Europe; HIV has only been present for a short time; the CCR5 mutation has been around for many years; the mutation is advantageous for something else.

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From the examiners' report: Under 5% got both marks. Use the context: there are fewer HIV infections in Europe, and HIV hasn't been in humans for long enough for selection to raise the frequency.

Question 18

A level Paper 1 · June 2022 · Q02.4 · 3 marks · Hard

Evaluate whether more trehalose in the diet could explain more antibiotic-resistant C. difficile infections.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 2: growth rate of non-resistant and antibiotic-resistant C. difficile on agar with no carbohydrate (both about 20 to 22 arbitrary units) and with trehalose (non-resistant about 19, resistant about 62).
Show the mark scheme Mark scheme, max 3 (max 2 from one side): for, resistant bacteria grow faster with trehalose, so increase in frequency and outcompete non-resistant ones; against, lab not people; other disaccharides or bacterial species may affect them; no statistical test; no data with both types growing together; only one trehalose concentration.

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From the examiners' report: Link Figure 2 to growth rate, not just 'more bacteria'. Note there's no statistical test, only one concentration and no data from people. 'Correlation isn't causation' scores nothing.

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

Each point below is followed by wording that gained marks.

  • Allele, not gene, every time: On the CEL question only around 20% scored 3 out of 4, and marks were lost by writing 'gene' rather than 'allele'. On the malaria question a 'resistance gene' wasn't credited where a 'resistance allele' was.

    ✔ Gains credit: "Mutation results in a new allele"; "individuals with the allele are more likely to survive and reproduce"; "increase in frequency of this allele in the population".

  • Antibiotics select; they don't cause mutations: On the hospital C. difficile question, examiners again saw antibiotic use given as the cause of mutations, and bacteria described as making an immune response with white blood cells and antibodies. The mark scheme rejects answers where antibiotics cause the resistance allele.

    ✔ Gains credit: "Some bacteria have alleles for resistance"; "antibiotics are the selection pressure: non-resistant bacteria die, resistant bacteria survive and reproduce".

  • Bacteria are resistant, never immune: On the penicillin-resistant S. aureus question about 5% got all 3 marks. A very common misconception was that bacteria become 'immune' to penicillin, and weaker answers wrote only about a 'beneficial allele'.

    ✔ Gains credit: "Resistant S. aureus are more likely to survive and reproduce to pass on the blaZ / penicillin-resistance allele"; "increased frequency of the blaZ allele in the next generation".

  • Name a type of selection from the specification: Slightly less than 50% named directional selection for penicillin resistance; 'mutation', 'survival of the fittest' and 'adaptations' were given instead. In the fish tank question students offered planned, continuous, artificial, systematic and statistical selection.

    ✔ Gains credit: "Directional"; "one extreme is selected / favoured / allowed to breed".

  • Keep the mutation in the right organism: On the malaria question 40% scored 3 or 4. Stock phrases about favourable alleles, with no mention of a mutation or of malaria, couldn't reach the first two marks, and some put the mutation in P. vivax. In the lactase question some thought lactase persistence was in the cattle.

    ✔ Gains credit: "Mutation produced an allele"; "those with the allele are less likely to get malaria / survive malaria"; "so are more likely to reproduce and pass on the allele".

  • Allele frequency, not allele number: The birth weight mark scheme does not accept 'number' for 'frequency', and the lactase scheme ignores an 'increase in number of allele'. On the penicillin question, allele frequency was poorly expressed, for example 'the majority of bacteria will have the allele'.

    ✔ Gains credit: "Alleles for extreme mass at birth decrease in frequency (proportion / percentage) in the population."

  • The scientists did the selecting: On the red clover question, many answers just described the outcome of directional selection, or said the environment had changed, instead of using the information that the scientists bred only from plants producing 2n gametes. 'Allele' in the right context was seen infrequently.

    ✔ Gains credit: "The scientists selected plants that produced 2n gametes for breeding; these plants passed on their alleles; the frequency of alleles for 2n gametes increased."

  • Check the y-axis before you evaluate: Just under half concluded that the fish tank evidence did not support the fishing nets, and only around 1% covered both sides. Many thought the nets reduced population size, when Figure 8 shows the mean mass of fish.

    ✔ Gains credit: "Not supported: fishing reduces the mean mass of fish because large fish are removed"; "but only one species was studied / no statistical test".

Download the questions

Download the PDF pack (18 questions, mark schemes at the end)

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

Tom Whitburn
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