AQA A Level Biology 4/5/6 mark | Strategies
Review of Key Quizzes with Solutions (Latest
2026/2027)
Introduction
AQA A-Level Biology 7402b they are aligned to the current AQA 7402
specification, which includes genetics, gene expression, inheritance,
mutation and practical/data-analysis skills. AQA also uses extended
responses requiring a coherent, logically structured line of reasoning.
Part A — Genetics & Gene Expression
### 1. [4 marks]
Explain how a mutation in the DNA base sequence can result in a
different protein.
**Answer:**
* Mutation changes the base sequence of a gene.
* This may change the sequence of bases in mRNA during transcription.
* Different mRNA codons may result in different amino acids being
incorporated.
* The altered amino-acid sequence can change the protein's tertiary
structure and function.
### 2. [5 marks]
,Explain why a substitution mutation may have no effect on the
phenotype.
**Answer:**
* A substitution changes one base for another.
* The genetic code is degenerate, meaning several codons can code for
the same amino acid.
* Therefore, the altered codon may still code for the same amino acid.
* The primary structure of the protein remains unchanged.
* Consequently, the protein may retain its normal structure and
function.
### 3. [6 marks]
Explain how a deletion mutation can have a greater effect on a protein
than a substitution mutation.
**Answer:**
* A deletion removes one or more bases from DNA.
* If the number deleted is not a multiple of three, the reading frame
changes.
* This is called a frameshift mutation.
* Every codon downstream of the mutation may therefore be altered.
* Different amino acids may be incorporated into the polypeptide.
* The resulting protein may have a different tertiary structure and lose
its function. ([AQA][2])
,### 4. [4 marks]
Describe the role of DNA in protein synthesis.
**Answer:**
* DNA contains genes that code for polypeptides.
* A gene is transcribed to produce mRNA.
* mRNA carries the genetic information to a ribosome.
* The ribosome uses the mRNA codons to determine the amino-acid
sequence.
### 5. [6 marks]
Explain how a gene is expressed in a cell.
**Answer:**
* A gene contains a specific base sequence.
* RNA polymerase binds to the DNA and produces a complementary
mRNA strand.
* The mRNA leaves the nucleus through a nuclear pore.
* It attaches to a ribosome.
* tRNA molecules carry specific amino acids and have complementary
anticodons.
* The amino acids are joined by peptide bonds to form a polypeptide.
, genui{"biology_genetics_evolution_ecology_learning_block":
{"type_id":"DNA_TRANSCRIPTION"}}
### 6. [5 marks]
Explain why cells in the same organism can have different structures and
functions even though they contain the same genome.
**Answer:**
* Most body cells contain the same genetic information.
* Different cells express different genes.
* Genes that are not required can be switched off.
* Different proteins are therefore produced in different cells.
* These proteins determine cell structure and function.
### 7. [4 marks]
Explain the relationship between a gene and a polypeptide.
**Answer:**
* A gene is a sequence of DNA bases.
* The sequence determines the sequence of bases in mRNA.
* mRNA codons determine the sequence of amino acids.
* The amino-acid sequence determines the structure and function of the
Review of Key Quizzes with Solutions (Latest
2026/2027)
Introduction
AQA A-Level Biology 7402b they are aligned to the current AQA 7402
specification, which includes genetics, gene expression, inheritance,
mutation and practical/data-analysis skills. AQA also uses extended
responses requiring a coherent, logically structured line of reasoning.
Part A — Genetics & Gene Expression
### 1. [4 marks]
Explain how a mutation in the DNA base sequence can result in a
different protein.
**Answer:**
* Mutation changes the base sequence of a gene.
* This may change the sequence of bases in mRNA during transcription.
* Different mRNA codons may result in different amino acids being
incorporated.
* The altered amino-acid sequence can change the protein's tertiary
structure and function.
### 2. [5 marks]
,Explain why a substitution mutation may have no effect on the
phenotype.
**Answer:**
* A substitution changes one base for another.
* The genetic code is degenerate, meaning several codons can code for
the same amino acid.
* Therefore, the altered codon may still code for the same amino acid.
* The primary structure of the protein remains unchanged.
* Consequently, the protein may retain its normal structure and
function.
### 3. [6 marks]
Explain how a deletion mutation can have a greater effect on a protein
than a substitution mutation.
**Answer:**
* A deletion removes one or more bases from DNA.
* If the number deleted is not a multiple of three, the reading frame
changes.
* This is called a frameshift mutation.
* Every codon downstream of the mutation may therefore be altered.
* Different amino acids may be incorporated into the polypeptide.
* The resulting protein may have a different tertiary structure and lose
its function. ([AQA][2])
,### 4. [4 marks]
Describe the role of DNA in protein synthesis.
**Answer:**
* DNA contains genes that code for polypeptides.
* A gene is transcribed to produce mRNA.
* mRNA carries the genetic information to a ribosome.
* The ribosome uses the mRNA codons to determine the amino-acid
sequence.
### 5. [6 marks]
Explain how a gene is expressed in a cell.
**Answer:**
* A gene contains a specific base sequence.
* RNA polymerase binds to the DNA and produces a complementary
mRNA strand.
* The mRNA leaves the nucleus through a nuclear pore.
* It attaches to a ribosome.
* tRNA molecules carry specific amino acids and have complementary
anticodons.
* The amino acids are joined by peptide bonds to form a polypeptide.
, genui{"biology_genetics_evolution_ecology_learning_block":
{"type_id":"DNA_TRANSCRIPTION"}}
### 6. [5 marks]
Explain why cells in the same organism can have different structures and
functions even though they contain the same genome.
**Answer:**
* Most body cells contain the same genetic information.
* Different cells express different genes.
* Genes that are not required can be switched off.
* Different proteins are therefore produced in different cells.
* These proteins determine cell structure and function.
### 7. [4 marks]
Explain the relationship between a gene and a polypeptide.
**Answer:**
* A gene is a sequence of DNA bases.
* The sequence determines the sequence of bases in mRNA.
* mRNA codons determine the sequence of amino acids.
* The amino-acid sequence determines the structure and function of the
