Mutations
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of DNA. You can test your knowledge on this below.
What is the structure of DNA made up of?
A sequence of nucleotide bases (adenine, thymine, cytosine, and guanine) joined by a sugar-phosphate backbone.
During which process are mutations most likely to occur?
DNA replication.
What enzyme is responsible for assembling nucleotides during replication?
DNA polymerase.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains mutations, or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What is a Mutation?
- A mutation is a change in the base sequence of DNA.
- Mutations can occur spontaneously and randomly, most often during DNA replication. We cannot predict where a mutation is going to take place.
- Mutations can involve:
- One base (a point mutation)
- A sequence of bases
Types of Gene (Base) Mutations
|
Mutation Type |
Description |
|
Addition (Insertion) |
One or more bases are inserted into the DNA sequence. |
|
Deletion |
One or more bases are removed from the sequence. |
|
Substitution |
A single base is swapped for a different base. |
|
Inversion |
A sequence of bases is reversed within the DNA strand. |
|
Duplication |
One or more bases are repeated. |
|
Translocation |
A sequence of bases is moved to a different position, which can be on the same or a different chromosome. |
Mutagenic Agents
Mutagenic agents increase the frequency at which mutations occur.
1. Physical Mutagens
Ionising radiation: e.g. X-rays, gamma rays, UV light.
2. Chemical Mutagens
Examples include:
Benzopyrene in cigarette smoke
Nitrous acid
Chemicals used in chemotherapy
3. Biological Agents
Certain viruses (e.g. HPV)
Key Terms
Mutation – a change in the DNA base sequence.
Gene mutation – mutation occurring in the base sequence of a gene.
Mutagen – a factor that increases the rate of mutation.
No answer provided.
Exam Tips
Mutations occur in the DNA and will lead to a different mRNA transcript and may lead to a different polypeptide.
Mutagenic agents increase the frequency of mutations, we cannot state where or when it will cause a mutation.
No answer provided.
Name and describe two types of gene mutation. (2 marks)
Substitution – one base is replaced by a different base in the DNA sequence.
Deletion – one or more bases are removed from the DNA sequence.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!