Practise 36 exam-style questions on Inherited disorders for AQA GCSE Biology. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
36 questions
2–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
State why polydactyly can appear in a child when neither parent shows polydactyly (phenotypically).
Model answer
New dominant mutation in the child's gene (de novo mutation) or one parent is mosaic / has a somatic mutation in germ cells.
Explanation
A dominant trait can arise spontaneously via a new mutation, or if a parent has germline mosaicism the mutant allele may be passed without the parent showing the trait.
Mark scheme
1 mark
New mutation (de novo) in child
1 mark
Parental germline mosaicism (less common) or mosaicism
Question 2
3 marks
Explain why cystic fibrosis only appears in children when both parents carry the recessive allele, using genetic terminology.
Model answer
CF is recessive; a person must have two copies of the mutant allele (ff) to show the disease. Carriers (Ff) do not show disease but can pass the allele to offspring. Two carriers have a 25% chance of producing an affected child.
Explanation
Recessive inheritance requires both alleles be the disease form; carriers are phenotypically normal but can produce affected children if both parents contribute the recessive allele.
Mark scheme
1 mark
CF is caused by a recessive allele
1 mark
Affected individuals must have two recessive alleles (ff)
1 mark
Carriers (Ff) can pass the allele on; two carriers give 25% affected offspring
Question 3
3 marks
Explain why a dominant allele like that for polydactyly can remain in a population despite being potentially disadvantageous.
Model answer
If the allele has mild effects or appears after reproductive age it may not reduce fitness significantly; heterozygote advantage or new mutations also maintain allele frequency; cultural factors may not select against it.
Explanation
Dominant alleles can persist if they do not reduce fitness, are reintroduced by mutation, or are maintained for other reasons such as advantage or social acceptance.
Mark scheme
1 mark
If trait is mild or not reducing reproductive success, allele persists
1 mark
New mutations introduce allele or heterozygote advantage may maintain it
1 mark
Cultural or social acceptance may not select against it
Question 4
4 marks
A country plans to offer national carrier screening for CF. Outline two public health steps needed to implement this responsibly.
Model answer
Ensure affordable and equitable access; provide counselling and education; set up lab quality control and follow-up services; monitor outcomes and ethics review.
Explanation
A responsible program includes counselling, access, lab quality, and oversight to ensure ethical, accurate, and equitable screening.
Mark scheme
1 mark
Provide counselling and education for informed choices
1 mark
Ensure equitable, affordable access and support services
1 mark
Set up quality-controlled labs and accurate testing
1 mark
Implement monitoring/ethics oversight and follow-up care
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