AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Gene mutations might arise during DNA replication. They include addition,…
Full specification wording
Alteration of the sequence of bases in DNA can alter the: Gene mutations might arise during DNA replication. They include addition, deletion, substitution, inversion, duplication and translocation of bases.
A gene mutation is a change in the base sequence of DNA.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 1 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A gene mutation is a change in the base sequence of DNA. These might arise spontaneously during DNA replication, for example if DNA polymerase inserts an incorrect nucleotide, producing a substitution. Other types arise through different errors: deletion removes a base and addition inserts one; unless the number changed is a multiple of three, this causes a frameshift, altering every subsequent triplet. Duplication repeats a section of bases. Inversion reverses a sequence of bases so its triplets are read backwards. Translocation moves a sequence of bases to a different position within the DNA sequence. These changes can alter the mRNA codons, potentially changing the amino acid sequence and the protein's tertiary structure.
What earns the marks
- Define a gene mutation as a change in the base sequence of DNA.
- State that gene mutations might arise spontaneously during DNA replication.
- Describe the specific mechanism of a named mutation type, such as substitution, addition, deletion, duplication, inversion, or translocation of bases.
- Explain that a mutation can change the sequence of amino acids in the encoded polypeptide.
- Explain that an altered amino acid sequence can change the position of hydrogen, ionic, and disulfide bonds, altering the protein's tertiary structure.
Common mistakes and how to put them right
Writing that 'different amino acids are formed'.
Put it right: State that a different amino acid is inserted, which changes the overall sequence or order of amino acids in the polypeptide.
Confusing a gene mutation with a chromosome mutation.
Put it right: Gene mutations involve changes to the DNA base sequence, whereas chromosome mutations involve changes in chromosome number or structure, such as deletion, duplication, inversion or translocation of chromosome segments.
Describing an inversion as a loss of bases.
Put it right: State that the bases are still present but their sequence is reversed.
Exam tips
- Open any mutation explanation by stating it is a 'change in the base sequence of DNA'.
- If asked to describe a named mutation, state the type and explicitly describe its effect on the DNA triplets (e.g., causing a frameshift).
- Always refer to a change in the 'sequence of amino acids' or 'primary structure' rather than just saying it makes a different protein.
Try the lesson
The start of the Alteration of the sequence of bases in DNA can alter the: Gene mutations might arise during DNA replication. They include addition, deletion, substitution, inversion, duplication and translocation of bases. lesson, made from checked teaching notes for this specification point.
Have a go first
Which type of gene mutation involves one base being replaced by a different base?
Listen
A gene mutation is a change in the base sequence of DNA. These might arise spontaneously during DNA replication, for example if DNA polymerase inserts an incorrect nucleotide, producing a substitution. Other types arise through different errors: deletion removes a base and addition inserts one; unless the number changed is a multiple of three, this causes a frameshift, altering every subsequent triplet. Duplication repeats a section of bases. Inversion reverses a sequence of bases so its triplets are read backwards. Translocation moves a sequence of bases to a different position within the DNA sequence. These changes can alter the mRNA codons, potentially changing the amino acid sequence and the protein's tertiary structure. A strong answer earns marks for these points. Define a gene mutation as a change in the base sequence of DNA. State that gene mutations might arise spontaneously during DNA replication. Describe the specific mechanism of a named mutation type, such as substitution, addition, deletion, duplication, inversion, or translocation of bases. Explain that a mutation can change the sequence of amino acids in the encoded polypeptide. A common slip: Writing that 'different amino acids are formed'. Instead, state that a different amino acid is inserted, which changes the overall sequence or order of amino acids in the polypeptide. Exam tip: Open any mutation explanation by stating it is a 'change in the base sequence of DNA'.
See it
Key words
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gene mutation
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DNA replication errors
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substitution and deletion
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frameshift
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See every definition
- gene mutation
- A change in the base sequence of DNA.
- DNA replication errors
- Mutations that might arise spontaneously during DNA replication, for example if DNA polymerase inserts an incorrect nucleotide, producing a substitution.
- substitution and deletion
- A substitution is produced when DNA polymerase inserts an incorrect nucleotide, while a deletion removes a base.
- frameshift
- Caused when the number of bases changed is not a multiple of three, altering every subsequent triplet.
Label the diagram
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