OCR GCSE Biology A: Stem cells, gene technology and genomics in medicine (J247)

This study guide covers statements B6.3v, B6.3w and B6.3x of OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018. They sit in topic B6.3, Monitoring and maintaining health, and ask you to weigh up medical technologies. None of the three statements is printed in bold in the specification text, so none is marked as Higher Tier only. Check your progress against the OCR GCSE Biology hub, the printable checklist and the free diagnostics. Then use the revision notes and the practice questions.

For what stem cells are and how cells differentiate, see the earlier membranes, mitosis and stem cells guide. For how genetic engineering works in farming, see genetic engineering and biotechnology in food. This page is about medicine only.

What this unit covers

Statement	What you must be able to do	Tier
B6.3v	Discuss potential benefits and risks of using stem cells in medicine, including tissue transplantation and rejection	Both tiers
B6.3w	Explain possible benefits and risks of gene technology in medicine, including practical and ethical considerations	Both tiers
B6.3x	Discuss the potential importance for medicine of our increasing understanding of the human genome, including predicting the likelihood of diseases occurring and treating them with drugs targeted to genomes	Both tiers

The command words “discuss” and “explain” mean you should give more than one side. A one-sided answer rarely covers what the question asks.

B6.3v: Stem cells in medicine

The idea

Stem cells are unspecialised: they keep dividing and can then differentiate into specialised cell types. Embryonic stem cells can become almost any cell type. Adult stem cells, such as those in bone marrow, make a narrower range of cell types. Medicine uses this to replace tissue that is damaged or missing.

Uses

• Bone marrow and blood stem cell transplants. For some leukaemias, treatment destroys the patient’s diseased bone marrow. Healthy donor stem cells are then given. They settle in the marrow and make new blood cells, including white blood cells.
• Research into repair of other tissues. Stem cells are being investigated for replacing damaged nerve, retina, heart muscle and insulin-making cells. Treat these as possible future benefits, not routine treatments.

Transplantation and rejection

Cells have antigens (proteins) on their surface. Your immune system recognises your own antigens as “self”. Donor cells carry different antigens, so your lymphocytes can treat them as foreign and attack them. This is rejection.

Ways to reduce it:

1. Match the tissue type. The closer the donor’s antigens are to yours, the weaker the response. Close relatives are more likely to match.
2. Immunosuppressant drugs. These weaken the response, but they leave the patient open to infection.
3. Use the patient’s own cells. Adult stem cells taken from the patient carry the patient’s antigens, so there is nothing foreign to attack.
4. Therapeutic cloning. The nucleus of one of the patient’s body cells is put into an egg cell whose nucleus has been removed. The cell is stimulated to divide and embryonic stem cells are taken from it. They are genetically identical to the patient, so they should not be rejected.

In bone marrow transplants, rejection can also run the other way. Donor white blood cells can attack the recipient’s body. This is called graft-versus-host disease.

Risks and issues

• Stem cells that keep dividing can form tumours.
• Donor material can carry viruses that infect the recipient.
• Cells may not differentiate into the right type, or may not work properly once in place.
• Collecting adult stem cells needs a procedure, which carries its own risk.
• Ethical objections: getting embryonic stem cells destroys an embryo. Some people think an embryo has the rights of a person. Others point out that the embryos used are often spare ones from IVF treatment that would be discarded, and that the potential to relieve suffering justifies using them.
• Cost and access: treatments may be expensive and available to few patients.

Worked example 1: the chance of a match

Each sibling has about a 1 in 4 chance of being a close tissue match for a patient. A patient has 3 siblings. What is the chance that at least one is a match?

1. Chance that one sibling is not a match = 3/4.
2. Chance that none of the 3 is a match = 3/4 × 3/4 × 3/4 = 27/64.
3. Chance that at least one is a match = 1 − 27/64 = 37/64 = 58% (to the nearest whole number).

So even with 3 siblings, the patient has less than a 6 in 10 chance of a family match. This is why donor registries and other sources matter.

Worked example 2: evaluating a trial

A trial treats 60 patients with an injected stem cell therapy and 60 with the standard treatment. After a year, 39 treated patients and 21 standard-treatment patients have improved. Serious side effects occur in 6 treated patients and 3 standard-treatment patients.

1. Improved with stem cells: 39/60 × 100 = 65%.
2. Improved with standard treatment: 21/60 × 100 = 35%.
3. Difference: 65 − 35 = 30 percentage points in favour of the stem cell therapy.
4. Serious side effects: 6/60 = 10% compared with 3/60 = 5%. The risk is twice as high.

Evaluation: the therapy helps more patients, but side effects are more common. The trial is small, ran for one year only, and says nothing about long-term risks such as tumours. A fair conclusion is that the results are promising and justify a larger, longer trial. They do not prove the therapy is safe.

B6.3w: Gene technology in medicine

Gene technology means changing the genes of cells or organisms. In medicine it is used in two main ways.

1. Making medicines

The human gene for insulin can be put into bacteria. The bacteria are grown in large fermenters and make human insulin, which is collected and purified for people with diabetes.

• Benefits: a large, reliable supply, no need to extract insulin from animal pancreases, and a product identical to human insulin.
• Risks and issues: strict manufacturing control is needed, and the product must be tested thoroughly. Some people have ethical concerns about moving human genes into other organisms.

2. Gene therapy

Gene therapy tries to treat a genetic disorder by giving cells a working copy of an allele. A modified virus (a vector) often carries the allele into the patient’s cells. Researchers have worked on disorders including severe combined immunodeficiency and cystic fibrosis. A gene-editing treatment for sickle cell disease and beta thalassaemia was licensed in the UK in 2023.

Benefits: it could treat the cause of a disorder, not only the symptoms, possibly with a single treatment.

Risks and practical considerations:

• The new allele may insert in the wrong place and switch on a gene that causes cancer. Some children in early trials for an immune disorder developed leukaemia.
• The immune system may attack the vector.
• The new allele may not be switched on enough, or the effect may fade, so treatment may need repeating.
• It is expensive and needs specialist centres.
• Long-term effects are unknown.

Ethical considerations:

• Changes made to body cells (somatic therapy) affect only the patient. Changes to egg, sperm or embryo cells would be passed to future generations who cannot consent. Heritable changes are tightly controlled and are not currently allowed in UK clinical use.
• Some people fear the technology could move from treating disease to choosing traits.
• Cost raises questions about who gets treated.

Worked example 3: judging a gene therapy trial

In a trial, 20 children with an inherited immune disorder receive gene therapy. After two years, 17 have normal immune function. Two develop leukaemia.

1. Success: 17/20 × 100 = 85%.
2. Leukaemia: 2/20 × 100 = 10%.
3. The benefit is large, because without treatment these children would face repeated severe infections. The risk is also serious, because leukaemia is life-threatening.
4. Judgement: the risk may be acceptable when the disorder is fatal and no other treatment works, but safer vectors are needed, and the numbers are too small to be sure of the true rates.

B6.3x: The human genome and medicine

The genome is all the genetic material of an organism. Sequencing the human genome means working out the order of the bases in human DNA. Sequencing is now much faster and cheaper than when the first human genome was completed. Understanding the genome has two main medical uses.

Predicting the likelihood of disease

Some alleles are linked to a higher risk of a disease. A genetic test can find them before symptoms appear, so a person can be offered screening, advice on lifestyle or early treatment.

Key points:

• A result usually gives a risk, not a certainty. Many diseases also depend on environment and lifestyle.
• A person may not want to know, because of anxiety or what it could mean for relatives, who share some of the same alleles.
• There are concerns about privacy and about insurers or employers using the information unfairly.
• A positive result may lead to treatment that was not needed. A negative result can give false reassurance.

Drugs targeted to genomes

Patients differ in their alleles, so they differ in how they respond to a drug. If a test shows which patients are likely to benefit, doctors can choose the right drug and dose. This avoids giving ineffective drugs and reduces side effects. Some cancer drugs work only on tumours with a particular genetic change, so the tumour is tested first.

Worked example 4: reading a risk

In a population, 12% of people develop disease X in their lifetime. Among people with allele Y, 60% do. In a town of 20 000 people, 1 in 400 carry allele Y.

1. Carriers: 20 000 ÷ 400 = 50.
2. Carriers expected to develop the disease: 60% of 50 = 30.
3. If carriers had the average risk: 12% of 50 = 6.
4. Extra cases linked to allele Y: 30 − 6 = 24.
5. Risk is 60 ÷ 12 = 5 times higher, but 40% of carriers (20 of 50) never develop the disease.

So the test is informative, but it cannot say who will become ill.

Worked example 5: a targeted drug

A drug is tested on 200 patients. 80 have a genetic marker and 120 do not. Of those with the marker, 56 respond. Of those without it, 18 respond.

1. With marker: 56/80 × 100 = 70%.
2. Without marker: 18/120 × 100 = 15%.
3. Overall: 74/200 × 100 = 37%.

The overall figure hides the difference. Testing for the marker would let doctors give the drug to patients likely to respond and look for alternatives for the rest.

Common errors

• Writing that stem cell treatment “cures” a disease without mentioning risk or limited evidence.
• Saying embryonic stem cells are rejected “because they are foreign” without naming antigens and the immune response.
• Saying immunosuppressants have no downside. They raise the risk of infection.
• Treating a genetic test result as a certain prediction.
• Giving only benefits, or only risks, in a “discuss” question.
• Mixing up gene therapy (treating a patient) with selective breeding or farm crop engineering.
• Saying ethical objections are “wrong” instead of explaining both viewpoints.

Using the evidence in an answer

Good answers give a benefit, a risk and a judgement that uses the information supplied. Quote figures from data in the question, compare like with like, and say what the data cannot show, such as long-term safety.

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Statements B6.3v, B6.3w and B6.3x.