Gene mutations as structural changes to genes at the molecular level
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Question
What is a mutation?
Answer
A **random change to the base sequence of DNA**.
Question
Why are mutations important for variation?
Answer
They are the **source of new alleles** — the ultimate origin of all genetic variation.
Question
How does a mutation create a new allele?
Answer
By **changing the base sequence** of an existing gene, producing a new version (allele) of it.
Question
What are the three types of gene mutation?
Answer
**Substitution**, **insertion** and **deletion**.
Question
Define a substitution mutation.
Answer
One base is **swapped for a different base**; the total number of bases stays the same.
Question
Define an insertion mutation.
Answer
An extra base is **added** into the sequence; the total number of bases increases.
Question
Define a deletion mutation.
Answer
A base is **removed** from the sequence; the total number of bases decreases.
Question
What is a frameshift, and which mutations cause it?
Answer
A shift in the reading frame so every codon downstream is read differently — caused by **insertion or deletion**.
Question
Why doesn't a substitution cause a frameshift?
Answer
Because it **does not change the number of bases** — the reading frame stays the same, so only one codon is affected.
Question
How can you classify a mutation from two base sequences?
Answer
**Count the bases**: same number (one letter different) = substitution; one more = insertion; one fewer = deletion.
Question
What is a mutagen? Give an example.
Answer
Anything that **increases the rate of mutation** — for example **UV light**, X-rays or certain chemicals.
Question
Are mutations always harmful?
Answer
**No** — they can be harmful, neutral or beneficial; they are random changes.
Question
Give one similarity between substitution and insertion.
Answer
Both are **random changes to the DNA base sequence** and both can produce a **new allele**.
Question
Give one difference between substitution and insertion.
Answer
Substitution **swaps** a base (number unchanged); insertion **adds** a base (number increases, causing a frameshift).
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Topic 4.3 hub
Mutations and gene editing
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