Lesson 3.8.4.2.1

3.8.4.2.1 DNA probes, hybridisation and genetic counselling Quiz: AQA Biology, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.8.4.2.1, DNA probes, hybridisation and genetic counselling: 20 multiple choice questions for the AQA Biology (7402), Unit 8: The control of gene expression, written with Revision Ninja.

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The 20 questions

  1. A DNA probe is best described as:

    • A double-stranded DNA sequence that is never labelled, so it can be detected only by sequencing the whole genome of the patient
    • An enzyme that cuts DNA at specific sites, which is used to release the target allele from the rest of the genome before analysis
    • A protein that binds to mRNA in the cytoplasm, which is used to block translation of the target gene in a diagnostic test
    • A labelled single-stranded DNA sequence complementary to the target allele

  2. DNA hybridisation is the process in which:

    • RNA is converted into DNA by reverse transcriptase
    • Complementary single strands of DNA join together by base pairing
    • Proteins are broken into amino acids
    • DNA strands are cut into short fragments by enzymes

  3. How are DNA probes usually labelled so that they can be detected?

    • With a primer that binds to the probe
    • With a radioactive or fluorescent tag
    • With a ribosome attached to the probe
    • With a restriction enzyme that cuts the probe

  4. DNA probes can be used to screen patients for:

    • Only changes in blood pressure
    • Only changes in body temperature
    • Heritable conditions, drug responses or health risks
    • Only bacterial infections

  5. How is information from DNA probes used in genetic counselling?

    • To advise families on the chance of inheriting or passing on a condition
    • To remove the faulty allele from the patient's body, so that the condition cannot be passed on to any of the patient's children in future
    • To replace the patient's ribosomes with healthy ones, so that the faulty proteins are no longer made in the patient's cells at all
    • To change the patient's phenotype directly by altering the expression of the gene in every cell of the patient's body in one treatment

  6. Personalised medicine is based on:

    • The same treatment being given to everyone regardless of genes
    • Using only plant-based drugs
    • Removing all genes from the patient's cells
    • Treatment chosen according to a patient's genetic profile

  7. A labelled probe binds to a target sequence because of:

    • Binding to the ribosome during translation
    • Random attraction between any two DNA molecules
    • Binding to the amino acids in a polypeptide
    • Base pairing between complementary sequences

  8. A patient's DNA hybridises with a labelled probe for a particular allele. What does this suggest?

    • The patient's mRNA has been destroyed
    • The patient's DNA contains no genes at all
    • The patient's DNA contains the sequence complementary to the probe
    • The patient has been treated with a restriction enzyme

  9. Why must a DNA probe be single-stranded?

    • So that it can be cut by restriction enzymes
    • So that it can pass through the nuclear membrane unchanged
    • So that it can base pair with the complementary target strand
    • So that it can be copied by PCR without primers

  10. What is the purpose of screening a patient's DNA for a drug response?

    • To change the patient's genome permanently, so that the drug can be given safely to every later generation of the family
    • To stop the drug from working in every patient, so that no one is ever given a treatment that might not suit them
    • To predict whether the patient is likely to respond to a drug or to suffer side effects
    • To produce the drug inside the patient's cells by switching on a gene, so that no tablets or injections are needed

  11. What information from a probe result is most useful for genetic counselling?

    • The number of ribosomes in the patient's cells, which can be counted from the probe signal and reflects their genetic risk
    • The colour of the patient's hair, since probes bind to pigment genes and so the hair colour shows which alleles are present
    • The patient's blood group only, because the blood group alone determines every genetic risk that a family needs to know about
    • Whether the person carries the allele and the risk of passing it on to offspring

  12. A probe screen tests 1000 people. If 2 per cent carry the allele, how many carriers are expected?

    • 50
    • 200
    • 2
    • 20

  13. Why should a positive probe result be interpreted with caution?

    • It shows the allele is present, but this does not always mean the disease will develop
    • It shows the person is not related to their family members, so the genetic counselling is no longer relevant to them
    • It shows the probe has damaged the person's DNA during the test, so the result must be discarded as a laboratory error
    • It proves the person has the disease with certainty, so no further clinical tests or medical advice are needed at all

  14. What does personalised medicine require from the patient?

    • A transplant of organs from another person
    • Genetic information that helps select the most suitable treatment
    • A change in the patient's blood group
    • Only a physical examination and no genetic data

  15. Which health risk can DNA probe screening help identify?

    • A susceptibility to a genetically determined condition
    • A risk of developing a sunburn
    • A risk of injury in a car accident
    • A risk of catching any infectious disease

  16. Why is screening individuals for genetically determined conditions ethically sensitive?

    • Results can lead to discrimination and require informed consent about how they will be used
    • Results change the patient's genome permanently, so every screened person must accept a changed genetic identity for life
    • Results are always wrong, so they can safely be ignored by doctors and the people who are screened for genetic conditions
    • Results can only be given to the patient's employer, who then decides which treatment the patient should receive in future

  17. A recessive disorder occurs in 1 in 10 000 births. How many affected births are expected in 50 000 births?

    • 50
    • 1
    • 5
    • 0.5

  18. Why must a DNA probe be complementary to the allele rather than the whole gene?

    • Probes must target sequence differences between alleles so that the alleles can be told apart
    • Probes must match the whole gene exactly to be detected at all, so a probe covering only part of a gene will never give a signal
    • Probes must be made of RNA, so they cannot target the DNA of a gene and are instead used only to detect proteins in blood
    • Probes always bind to proteins and never to DNA, so the test must use a protein that differs between the alleles of the gene

  19. Put these steps in the most likely order: 1 extract DNA, 2 denature the DNA into single strands, 3 apply the labelled probe, 4 wash and detect the hybridised probe. Which sequence is correct?

    • 2, 1, 3, 4
    • 4, 1, 2, 3
    • 1, 2, 3, 4
    • 1, 3, 2, 4

  20. Why is probe-based screening considered personalised yet limited?

    • It tests only known alleles, so it cannot detect unknown variants
    • It cannot be used for any patient with a known allele
    • It always identifies every genetic variant in a patient
    • It is never personalised because all patients receive the same test

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