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A labelled probe detects complementary sequence under controlled conditions. Interpret what that match means for an allele, a risk prediction and a person’s choices.
Video by Cognito. Foundation recap: the written lesson develops the A-level detail.
Viewing focus: Explain hybridisation with labelled DNA probes
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Probe binding depends mainly on:
Complementary base pairing. Sequence matching underlies hybridisation.
After watching 2: The probe’s label is used to:
Detect where binding has occurred. Detection is distinct from sequence alteration.
What you'll be able to do
A DNA probe is a short labelled sequence designed to bind to a complementary target. The sample DNA is made accessible as single strands and the probe hybridises where suitable base pairing occurs. A fluorescent or other detectable label reveals retained probe binding after appropriate treatment and washing.
Binding conditions affect specificity: very similar sequences may also bind under less stringent conditions. Positive and negative controls and a known reference help determine whether a signal reflects the intended target. A probe is a detection tool, not an enzyme that automatically repairs the allele it finds.
A probe can help identify a particular allele associated with a heritable condition or drug response. Whether that allele predicts disease depends on dominance, penetrance, other genes and environmental influences in the case provided. The assay’s accuracy also limits the conclusion.
A negative result for one allele does not exclude every possible genetic cause of a similar condition. A positive risk marker does not always mean inevitable disease. Distinguish finding a sequence from understanding its effect on protein, cell function and phenotype.
Genetic counselling can help individuals understand the meaning, uncertainty and family implications of results. Personalised-response information may help evaluate which intervention is more likely to be effective or cause adverse responses, but the strength of the supporting association and functional evidence matters.
Consider informed consent, confidentiality, potential anxiety, uncertain findings, access and the implications for relatives. Screening programmes need evidence on false positives, false negatives and useful consequences of finding the result. Present benefits and limitations together rather than assuming more sequence information always gives a clear decision.
Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.
Common mistakes to avoid
Key takeaways
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.