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Could we treat disease by fixing the faulty gene itself, or by growing fresh, healthy cells?

Outline the principles of gene therapy and the use of stem cells in medicine, and discuss their potential and limitations

A focused answer to the O-Level outcome on gene therapy and stem cells. Replacing faulty genes, what stem cells are, how each could treat disease, and the limitations and concerns.

Generated by Claude Opus 4.89 min answerUpdated 2026-06-06

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking
The answer
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What this dot point is asking

This outcome asks you to outline two cutting-edge medical approaches, gene therapy and stem cells, and to discuss their potential and limitations. Both aim to treat the cause of disease rather than just the symptoms, but both face real practical and ethical challenges, and examiners want a balanced answer.

The answer

Gene therapy

Gene therapy treats a disorder by inserting a working copy of a gene into a patient's cells to replace or make up for a faulty gene.

A faulty gene fails to make a working protein, which causes the disorder.
A working copy of the gene is delivered into the patient's cells, often using a vector such as a harmless modified virus.
If the cells express the working gene, they make the correct protein, and the symptoms can be reduced or prevented.

Stem cells

Stem cells are unspecialised cells that can divide to make more stem cells and can develop into different specialised cell types.

This ability to become many cell types is what makes them valuable.
They could be used to replace damaged or diseased cells and tissues, for example repairing nerve, heart or skin tissue, or growing tissue for transplant. This is regenerative medicine.

The potential

Together, these approaches could treat conditions that current medicine can only manage, by fixing the faulty gene or replacing the lost cells, rather than just easing symptoms.

The limitations and concerns

Delivery is difficult. Getting a gene into enough of the right cells, and keeping it working, is hard.
Safety risks. Inserted genes or transplanted cells might behave unpredictably, for example growing uncontrollably or being rejected.
Ethical concerns. Some stem cells are taken from early embryos, which many people object to. There are also worries about altering genes that could be passed to future generations.

Deciding on an approach for a patient

A patient has a genetic disorder where a faulty gene fails to make a needed protein, and also has damaged tissue from the disease. Work through which biotechnology approach could address each problem and what limits it.

Step 1: Address the faulty gene

The disorder is caused by a faulty gene, so gene therapy is relevant: deliver a working copy of the gene, via a vector such as a modified virus, so the cells can make the correct protein.

Step 2: Address the damaged tissue

The damaged tissue needs replacing with healthy cells. Stem cells could be guided to develop into the right cell type to repair or replace the tissue.

Step 3: Identify the limitations

For gene therapy, the gene must reach enough of the right cells and keep working, which is difficult. For stem cells, the cells must develop correctly, avoid rejection, and not grow uncontrollably; some sources also raise ethical concerns.

Step 4: Give a balanced conclusion

Both approaches could treat the cause, the faulty gene and the lost cells, but each faces delivery, safety and ethical challenges. A balanced answer naming the approach, its action and its limit is exactly what the question rewards.

Examples in context

Example 1. Treating an inherited immune disorder. In some inherited disorders where a single gene is faulty, gene therapy has been used to deliver a working copy into the patient's cells, allowing them to make the missing protein. It shows the principle working in practice, for carefully chosen single-gene conditions.

Example 2. Growing skin for burns. Stem cells from a patient can be grown into sheets of new skin to treat severe burns. Because the cells are the patient's own, rejection is less of a problem, illustrating regenerative medicine and one way around a key limitation.

Try this

Q1. State the principle of gene therapy. [1 mark]

Cue. Inserting a working copy of a gene into a patient's cells to replace or make up for a faulty gene.

Q2. Explain why stem cells are valuable in medicine. [2 marks]

Cue. They are unspecialised cells that can divide and develop into different specialised cell types, so they could replace damaged or diseased cells and tissues.

Q3. Give one ethical or practical concern about gene therapy or stem cells. [1 mark]

Cue. Some stem cells come from early embryos (ethical), or inserted genes and transplanted cells may behave unpredictably or be rejected (practical).

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksExplain the principle of gene therapy and outline how it could be used to treat a genetic disorder caused by a faulty gene.

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Examiners want the principle of supplying a working gene and an outline of delivery.

Gene therapy is the treatment of a disorder by inserting a working (healthy) copy of a gene into a patient's cells to replace or make up for a faulty gene. The faulty gene fails to make a working protein, causing the disorder, so supplying a functional gene allows the cells to make the correct protein.

A working copy of the gene is delivered into the patient's cells, often using a vector such as a harmless modified virus, which inserts the gene into the cells. If the cells then express the working gene and make the correct protein, the symptoms of the disorder can be reduced or prevented.

What markers reward: gene therapy as inserting a working gene to replace or compensate for a faulty one, the idea that the faulty gene fails to make a working protein, delivery using a vector such as a modified virus, and the cells then expressing the gene to make the correct protein.

Original5 marksDescribe what stem cells are and explain why they are valuable in medicine, giving one limitation or ethical concern.

Show worked answer →

The answer should define stem cells, explain their value, and give a limitation or concern.

Stem cells are unspecialised cells that can divide to produce more stem cells and can develop into different specialised cell types. This ability is what makes them valuable.

They are valuable in medicine because they could be used to replace damaged or diseased cells and tissues, for example to repair damaged nerve, heart or skin tissue, or to grow tissues for transplant. This is the basis of regenerative medicine.

One limitation or concern: some stem cells are obtained from early embryos, which raises ethical objections; there are also practical difficulties such as making sure the cells develop correctly and are not rejected or do not grow uncontrollably.

What markers reward: stem cells as unspecialised cells that can divide and develop into specialised cell types, their value in replacing damaged cells and tissues (regenerative medicine), and one valid limitation or ethical concern.