How can we read and use genetic information to treat and screen for disease?
The principles of gene therapy and gene technology, genetic screening and prenatal testing, and the social and ethical issues raised by using genetic information.
An Edexcel A-Level Biology B (Salters-Nuffield) answer on gene technology and screening, covering gene therapy, genetic screening and prenatal testing, the use of genetic information, and the social and ethical issues these raise.
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What this dot point is asking
Edexcel wants you to describe the principles of gene therapy and gene technology, explain genetic screening and prenatal testing, and discuss the social and ethical issues raised by using genetic information, using cystic fibrosis as the context. Mark schemes reward precise mechanism (how the gene gets in) and a balanced ethical argument.
Gene therapy
For cystic fibrosis, a normal CFTR allele can be packaged into a vector (such as a liposome or modified virus) and delivered to the epithelial cells of the lungs, usually as an inhaled aerosol. The vector carries the allele into the cell, which then transcribes and translates it to make functional CFTR channels. Somatic gene therapy treats only body cells, so the effect is not inherited and is often temporary because treated cells are replaced over time. Germ-line therapy would alter gametes or an early embryo and be passed to future generations; it is not generally permitted because the changes are irreversible and consent from those future generations is impossible.
Genetic screening and prenatal testing
- Genetic screening tests a person own DNA for disease-causing alleles, for example to identify carriers of cystic fibrosis before they have children, or to test newborns (the heel-prick test).
- Prenatal testing checks a fetus: amniocentesis samples amniotic fluid (around 15 weeks) and chorionic villus sampling (CVS) samples placental tissue (earlier, around 11 weeks). Both extract fetal cells whose DNA is analysed; both carry a small risk of miscarriage (roughly ).
- Preimplantation genetic diagnosis (PGD) tests embryos created by IVF before implantation, so only unaffected embryos are implanted, avoiding a decision about termination.
Social and ethical issues
Genetic information raises questions about consent and privacy (who can see the results, and could they be used against you), discrimination (by insurers charging higher premiums or employers refusing jobs), psychological impact (anxiety from knowing future disease risk), and difficult decisions about pregnancy after a positive prenatal test, including the ethics of selecting embryos. There are no simple answers, so good exam responses weigh the benefits (informed choice, early treatment, reduced suffering) against the risks and respect personal autonomy.
Examples in context
Example 1. Newborn screening for cystic fibrosis. In the UK the newborn blood-spot (heel-prick) test screens for cystic fibrosis and several other conditions in the first week of life. Early diagnosis means treatment (physiotherapy, enzyme supplements, prophylactic antibiotics) can start before lung damage occurs, improving life expectancy. This shows screening delivering clear benefit, with the trade-off that some results are false positives causing parental anxiety.
Example 2. PGD and saviour siblings. Couples using IVF can use PGD to select an embryo free of cystic fibrosis, and in rare cases to select one that is also a tissue match for an existing sick sibling (a saviour sibling). This delivers a clear medical benefit but raises sharp ethical questions about selecting embryos for the benefit of another person, which is exactly the kind of balanced debate examiners want.
Try this
Q1. Explain why somatic gene therapy is not passed on to a patient's children. [2 marks]
- Cue. It alters body (somatic) cells only, not the gametes, so the corrected gene is not inherited.
Q2. Suggest one social issue raised by genetic screening for cystic fibrosis. [1 mark]
- Cue. For example, the risk of genetic discrimination by insurers, or concerns about privacy of the results.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksDescribe how a working copy of the CFTR gene could be delivered to the epithelial cells lining the airways of a person with cystic fibrosis.Show worked answer →
Markers want the mechanics of somatic gene therapy.
A working CFTR allele is inserted into a vector, such as a liposome (a lipid sphere) or a modified harmless virus. The vector is delivered to the lungs, often as an aerosol that is inhaled so it reaches the epithelial cells. The liposome fuses with the cell surface membrane, or the virus injects its contents, carrying the CFTR allele into the cell. The cell then transcribes and translates the gene to make functional CFTR channels, restoring chloride ion transport.
Award marks for: working allele in a vector (liposome or virus named), aerosol delivery to airway epithelium, vector enters cell, cell expresses gene to make functional channels.
Edexcel 20236 marksEvaluate the use of prenatal genetic testing by amniocentesis for cystic fibrosis.Show worked answer →
An evaluate question: benefits, drawbacks and a judgement.
Benefits: it gives parents accurate information about whether the fetus is affected, allowing them to prepare for a child with the condition, arrange early treatment, or make an informed decision about the pregnancy. Drawbacks: amniocentesis carries a small risk of miscarriage (around ); a positive result forces difficult ethical decisions about termination; results may cause anxiety; and there are concerns about privacy and possible discrimination. Judgement: the test provides valuable information and respects parental autonomy, but because it carries a procedural risk and raises serious ethical choices it should be offered with full counselling and informed consent rather than routinely.
Markers reward at least two benefits, two drawbacks, and a reasoned judgement that weighs them.
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Sources & how we know this
- Pearson Edexcel A-Level Biology B (9BN0) specification — Pearson Edexcel (2015)