8.4.9The Control of Gene Expression (A Level only)

Genetic Counselling and Personalised Medicine — AQA A Level Biology 7402 Revision Notes & Topical Questions

5 min read 9 parts Lesson 29 of 34 1 quiz

📚 AQA A Level Biology 7402 Hub / Topical Revision

0%read

Lesson summary

8.4.9 Genetic Counselling and Personalised Medicine — AQA A Level Biology 7402 notes: Explain the role of genetic counselling and how knowledge of a patient's genome allows treatment to be tailored.Genetic counselling is the process of advising individuals and families about inhe…

non-directive
confidentiality
Personalised (precision) medicine
drug-metabolising enzymes
pharmacogenomics
Exam-style question 1

Section 1 of 9Genetic counselling

Genetic counselling is the process of advising individuals and families about inherited conditions: the chance of having or passing on the condition, the options available, and the implications of each.

Pedigree

A counsellor will usually construct a family pedigree, explain the mode of inheritance, and calculate risks.

For an autosomal recessive condition where both parents are carriers, each child has a 1 in 4 chance of being affected, a 1 in 2 chance of being an unaffected carrier,

and a 1 in 4 chance of being unaffected and not a carrier.

For a dominant condition such as Huntington's disease, a child of an affected heterozygous parent has a 1 in 2 chance of inheriting the allele.

Section 2 of 9What counselling involves

Explaining test results in non-technical language, including the accuracy and limits of the test.

Discussing reproductive options, such as prenatal testing, embryo selection, donor gametes, adoption or accepting the risk.

Supporting people who find out they carry or will develop a condition, and helping relatives decide whether they want testing.

Non-directive

Remaining non-directive: the counsellor presents information and the individual makes the decision.

Confidentiality

Maintaining confidentiality, although there can be a difficult balance if relatives are also at risk.

Counselling is offered before testing, so that a person understands what the result might mean, and again afterwards. Referral is common when there is a known family history, when both partners are from a group with a high carrier frequency, when there has been an affected child, or when a screening test is positive.

Section 3 of 9Personalised medicine

Personalised (precision) medicine uses a person's genome, or that of a tumour, to choose the best drug and dose. The reasons are:

Personalised medicine

Drug-metabolising enzymes

Alleles for drug-metabolising enzymes vary.

Some people break down a drug too quickly, so there is no effect at the standard dose, or too slowly, so it builds up to toxic levels.

Receptors

Alleles for receptors or other drug targets vary, so a drug that binds well in some people may not in others.

Cancer cells carry specific mutations.

For example, tumours with an overactive receptor can be treated with drugs that block that receptor, and a test shows which patients will respond.

Advantages are improved effectiveness, fewer side-effects and less waste of costly treatment. The study of how genes affect drug response is called pharmacogenomics, and the information can also guide the development of new drugs aimed at particular genotypes.

Section 4 of 9Challenges

Whole-genome tests are costly and produce large amounts of data that need expert interpretation.

A person's genotype is only one factor, since age, diet, other drugs and the environment also alter response.

Patients may be told of unexpected risks that they did not want to know about.

Data must be stored securely, and there are concerns over misuse by insurers or employers.

Health services must decide how to fund the testing fairly, and some populations are under-represented in genetic databases,

so predictions may be less accurate for them.

Section 5 of 9Linking ideas

This topic connects to inheritance (pedigrees and probabilities), gene mutation, cancer and tumour suppressor genes (gene expression and cancer), and gene technologies such as probes and sequencing in the two previous lessons. For exam questions, be ready to move from a genetic cross to a clinical decision: first state the genotypes, then the probability, then what that means for the family.

Section 6 of 9Worked example: calculating risk

A couple are both heterozygous carriers (Cc) of the cystic fibrosis allele.

Worked example: calculating risk

The gametes from each parent are C or c with equal probability, so the cross gives CC : Cc : cc in the ratio 1 : 2 : 1.

The probability of an affected child (cc) is 1/4.
If a child is known to be unaffected, the probability that the child is a carrier is 2 out of the 3 unaffected outcomes, which is 2/3.
This conditional step is often missed.

For an X-linked recessive condition such as haemophilia, a carrier mother has a 1 in 2 chance of passing the allele to each child,

so each son has a 1 in 2 chance of being affected and each daughter a 1 in 2 chance of being a carrier.

A counsellor presents such figures as chances for each pregnancy, not as predictions: the same 1 in 4 risk applies independently every time,

so an affected first child does not make the next child unaffected.

Section 7 of 9Exam-style questions

Two healthy parents have a child with cystic fibrosis. Explain why they might seek genetic counselling before having another child and state the probability that the next child is affected. [3]3 marks
Explain how personalised medicine could improve cancer treatment. [3]3 marks

Section 8 of 9Key terms

Term	Meaning
Genetic counselling	Advice to families about inherited conditions and risks
Pedigree	Family tree showing inheritance of a trait
Non-directive	Giving information without telling the person what to choose
Personalised medicine	Treatment tailored to an individual's genetic makeup
Pharmacogenomics	Study of how genes affect response to drugs
Carrier	Heterozygote with one copy of a recessive allele

Section 9 of 9Exam technique

Assuming counsellors tell people what to do: they are non-directive.

Saying that the chance of a carrier child is 1 in 4 for two carrier parents: it is 1 in 2 for a carrier, 1 in 4 for affected and 1 in 4 for unaffected non-carrier.

Saying personalised medicine cures genetic diseases: it tailors drugs and doses.

Ignoring non-genetic factors in drug response.

Last updated: 18 October 2026