AQA GCSE Biology Biology Paper 2 (Foundation), June 2022: Question 1

9 marks · Low Demand difficulty · Short Answer

Answer questions on the inheritance of maple syrup urine disease (MSUD), including completing a Punnett square and identifying genetic terms and biological molecules.

Practise this question

Question

Question 01 consists of eight parts regarding the inheritance of maple syrup urine disease (MSUD), a recessive condition. It includes a family pedigree tree (Figure 1) showing parents labeled 1 and 2, and three children labeled 3, 4, and 5, where child 3 is a female with MSUD, child 4 is an unaffected male, and child 5 is an unaffected female. A Punnett square grid (Figure 2) is shown for crossing heterozygous parents Nn and Nn. Questions ask for the definition of a recessive allele, interpretation of family pedigree symbols, completion of the Punnett square, phenotype of genotype Nn, percentage of offspring with MSUD, the term describing allele N (dominant), the chemical substance alleles are made of (DNA), and which dietary component is made of amino acids.
Question text

01 Maple syrup urine disease (MSUD) is a rare inherited human condition.

The allele for MSUD is recessive.

01.1 What is a recessive allele?

[1 mark]

Tick ( ) one box.

An allele expressed only if a person has two copies of the allele

An allele expressed only if it is inherited from the male parent

An allele expressed when it is found on only one of the chromosomes

Figure 1 shows the inheritance of MSUD in one family.

Figure 1

01.2 The symbol is not in the key for Figure 1.

What would this symbol represent?

[1 mark]

Persons 1 and 2 in Figure 1 have a child with MSUD and some children

without MSUD.

01.3 Complete Figure 2 to show the possible genotypes of the children.

Use the following symbols:

N = allele for not having MSUD

n = allele for MSUD

[2 marks]

Figure 2

Person 2

N n

N Nn

Person 1

n

01.4 What is the phenotype of a person with the genotype Nn?

[1 mark]

01.5 What percentage of the offspring in Figure 2 will have MSUD?

[1 mark]

Tick ( ) one box.

25% 50% 4 75% 100%

01.6 Which scientific term describes the allele N?

[1 mark]

Tick ( ) one box.

Dominant

*03* Genetic

Heterozygous

01.7 Alleles are found in the nucleus of a cell.

What chemical substance are alleles made from?

[1 mark]

01.8 People with MSUD must eat a special diet to reduce their intake of some types of

amino acid.

Which component of the diet is made of amino acids?

[1 mark]

Tick ( ) one box.

Carbohydrates

Minerals

Proteins

Mark scheme

Show the mark scheme Mark scheme for Question 01 with 9 total marks. 01.1: 'an allele expressed only if a person has two copies of the allele' (1 mark). 01.2: 'male with MSUD' (1 mark). 01.3: Punnett square completion showing NN, Nn, and nn (2 marks for 3 correct, 1 mark for 1 or 2 correct). 01.4: 'does not have MSUD' or healthy/unaffected (1 mark). 01.5: '25%' (1 mark). 01.6: 'Dominant' (1 mark). 01.7: 'DNA' or deoxyribonucleic acid (1 mark). 01.8: 'Proteins' (1 mark).

Question 1

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 an allele expressed only if a 1 AO1

person has two copies of the 4.6.1.6

allele

AO /

Spec. Ref.

01.2 male with MSUD allow equivalent statements eg 1 AO3

affected male or MSUD male or 4.6.1.6

man with the disease 4.6.1.7

AO /

Spec. Ref.

01.3 2 AO2

4.6.1.6

mark with 4.6.1.7

3 correct = 2 marks

01.4, 01.5

2 or 1 correct = 1 mark

AO /

Spec. Ref.

01.4 does not have MSUD allow equivalent statements – 1 AO2

mark with eg normal or not affected or 4.6.1.6

01.3, 01.5 healthy 4.6.1.7

ignore carrier

AO /

Spec. Ref.

01.5 correct percentage from if no answer in question 01.3 1 AO3

mark with Figure 2 allow 25% 4.6.1.6

01.3, 01.4 4.6.1.7

AO /

Spec. Ref.

01.6 dominant 1 AO2

4.6.1.6

AO /

Spec. Ref.

01.7 DNA allow deoxyribonucleic acid 1 AO1

allow nucleotide(s) 4.6.1.4

4.6.1.6

AO /

Spec. Ref.

01.8 proteins 1 AO2

4.6.1.4

Total Question 1 9

How to answer it

Inheritance, Genetic Crosses & Biological Molecules

📌 What this question tests

This 9-mark foundation/standard question assesses your core understanding of genetics and basic biochemistry:

  • Genetic terminology: Recessive, dominant, genotype, and phenotype.
  • Pedigree trees: Interpreting symbols representing sex and disease status.
  • Punnett squares: Predicting offspring genotypes and calculating probability/percentages.
  • Biomolecules: Recalling that alleles are made from DNA and that amino acids are the building blocks of proteins.

Question 01.1

Definition of a Recessive Allele (1 Mark)

✅ Correct Answer

Tick the first box:

"An allele expressed only if a person has two copies of the allele"

💡 Key Knowledge

  • A recessive allele needs two identical copies ( homozygous , e.g. nn ) to be expressed in the phenotype.
  • A dominant allele needs only one copy to be expressed (e.g. Nn or NN ).
Mark allocation: 1 mark for selecting the correct tick-box statement.

Question 01.2

Interpreting Family Pedigree Charts (1 Mark)

✅ Correct Answer

Male with MSUD

Also accepted: affected male, MSUD male, man with the disease.

🧠 Exam Technique

Look carefully at the key provided in the question:

  • Square = Male
  • Circle = Female
  • Shaded = Has the condition (MSUD)
  • Unshaded = Does not have MSUD

Combining a filled shape + square gives male with MSUD.

❌ Common Errors

  • Writing just "male" (misses the disease status).
  • Writing just "has MSUD" (misses the sex). Both elements are needed!
Mark allocation: 1 mark for clearly identifying both sex (male) and condition (with MSUD).

Question 01.3

Completing the Genetic Cross (2 Marks)

✅ Correct Completed Punnett Square

Person 2
N n
Person 1 N NN Nn (given)
n Nn nn

Missing genotypes to fill in: NN , Nn , nn

🧠 How Marks Are Awarded

  • All 3 boxes correct: 2 marks
  • 1 or 2 boxes correct: 1 mark
  • Convention tip: Always write the capital letter first (write Nn rather than nN ), though examiners will accept either order.
Mark allocation: 2 marks for 3 correct; 1 mark for 1 or 2 correct.

Question 01.4

Determining Phenotype from Genotype (1 Mark)

✅ Correct Answer

Does not have MSUD

Also accepted: normal, healthy, not affected.

💡 Key Knowledge

Genotype is the combination of alleles ( Nn ).
Phenotype is the observable physical characteristic.

Since allele N (not having MSUD) is dominant over n (having MSUD), the individual will not suffer from the condition.

❌ Common Errors

Writing "carrier" alone. While they are a carrier genetically, "carrier" is not their physical symptom/phenotype. The mark scheme states "ignore carrier".

Mark allocation: 1 mark for stating they do not have the condition.

Question 01.5

Calculating Probability & Percentage (1 Mark)

✅ Correct Answer

Tick the box for: 25%

📐 Step-by-Step Probability

  1. Identify which genotype causes MSUD: nn (homozygous recessive).
  2. Count how many boxes contain nn : exactly 1 out of 4 boxes.
  3. Convert fraction to percentage:
    (1 ÷ 4) × 100 = 25%
Mark allocation: 1 mark for 25% (or ecf from an incorrectly drawn grid in 01.3).

Question 01.6

Naming Allele Type (1 Mark)

✅ Correct Answer

Tick the box for: Dominant

💡 Why is allele N dominant?

The question states MSUD is caused by a recessive allele ( n ). Therefore, the normal allele ( N ) that masks it must be dominant.

Remember: Alleles are single letters, so an individual allele cannot be "heterozygous" (a term describing a two-allele pair like Nn ).

Mark allocation: 1 mark for selecting "Dominant".

Questions 01.7 & 01.8

Cell Biology & Dietary Molecules (2 Marks)

✅ 01.7: Allele Composition

DNA

Also accepted: deoxyribonucleic acid, nucleotide(s).

Tip: Alleles are alternative forms of a gene, and genes are short sections of DNA.

✅ 01.8: Amino Acid Polymer

Tick the box for: Proteins

Recall:
• Amino acids join to make proteins.
• Simple sugars join to make carbohydrates.

Mark allocation: 1 mark for DNA; 1 mark for Proteins.

Topics

Biology · B6: Inheritance, Variation and Evolution

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Foundation), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.