AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
They can arise spontaneously during DNA replication and include base…
Full specification wording
Genetic diversity can arise as a result of mutation or during: They can arise spontaneously during DNA replication and include base deletion and base substitution.
Mutations can arise spontaneously as copying errors during DNA replication.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mutations can arise spontaneously as copying errors during DNA replication. A base substitution replaces one base with another, affecting one triplet only. It may be silent because the genetic code is degenerate, meaning the new codon can still specify the same amino acid. Alternatively, a different amino acid may be inserted, which can alter the tertiary structure, or the triplet may become a stop codon. A base deletion removes a base, causing every base after it to shift back into a new triplet. This frameshift means that most codons downstream are altered, so most amino acids after the deletion are changed and the protein is often non-functional. Because of this frameshift effect, deletions are usually more damaging to the final polypeptide than substitutions.
What earns the marks
- Mutations can arise spontaneously as errors during DNA replication.
- A base substitution involves one base being replaced by a different base, affecting one triplet only.
- A base deletion involves a base being removed so that all subsequent triplets are shifted, causing a frameshift.
- A deletion changes most amino acids after the point of mutation, so the resulting protein is often non-functional.
- A substitution may not change the amino acid sequence because the genetic code is degenerate.
Common mistakes and how to put them right
Saying a substitution causes a frameshift, when only insertions and deletions shift the reading frame.
Describing spontaneous mutation as being caused by the organism's need to adapt to an environment.
Confusing a base deletion (a gene mutation) with a chromosome deletion or with non-disjunction.
Exam tips
- If asked to compare the two types of mutation, contrast their scope: a substitution affects one triplet, whereas a deletion affects every triplet downstream.
- Demonstrate a frameshift in application questions by rewriting the sequence in threes both before and after the deletion.
Try the lesson
The start of the Genetic diversity can arise as a result of mutation or during: They can arise spontaneously during DNA replication and include base deletion and base substitution. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is a type of gene mutation that can arise spontaneously during DNA replication?
Listen
Mutations can arise spontaneously as copying errors during DNA replication. A base substitution replaces one base with another, affecting one triplet only. It may be silent because the genetic code is degenerate, meaning the new codon can still specify the same amino acid. Alternatively, a different amino acid may be inserted, which can alter the tertiary structure, or the triplet may become a stop codon. A base deletion removes a base, causing every base after it to shift back into a new triplet. This frameshift means that most codons downstream are altered, so most amino acids after the deletion are changed and the protein is often non-functional. Because of this frameshift effect, deletions are usually more damaging to the final polypeptide than substitutions. A strong answer earns marks for these points. Mutations can arise spontaneously as errors during DNA replication. A base substitution involves one base being replaced by a different base, affecting one triplet only. A base deletion involves a base being removed so that all subsequent triplets are shifted, causing a frameshift. A deletion changes most amino acids after the point of mutation, so the resulting protein is often non-functional. Exam tip: If asked to compare the two types of mutation, contrast their scope: a substitution affects one triplet, whereas a deletion affects every triplet downstream.
See it
Key words
Say what each word means before you turn the card.
base substitution
Try answering aloud or in your head before turning the card.
base deletion
Try answering aloud or in your head before turning the card.
frameshift
Try answering aloud or in your head before turning the card.
degenerate code
Try answering aloud or in your head before turning the card.
See every definition
- base substitution
- One base is replaced by a different base, affecting one triplet only.
- base deletion
- A base is removed so that all subsequent triplets are shifted, causing a frameshift.
- frameshift
- Every base after a deletion shifts back into a new triplet, so most codons downstream are altered.
- degenerate code
- The genetic code is degenerate, meaning a new codon can still specify the same amino acid.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Genetic diversity can arise as a result of mutation or during: They can arise spontaneously during DNA replication and include base deletion and base substitution.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge