By the end of this lesson
- Define mutation.
- Describe causes of DNA sequence change.
- Distinguish somatic and germline mutation consequences.
BIG QUESTION
Where do genuinely new genetic variants come from?
Mutation introduces new sequences; selection and reproduction change their frequencies.
Mutation changes DNA sequence
A mutationA change in the base sequence of DNA, or in the structure or number of chromosomes, which may produce a new allele. is a change in DNA base sequence. It can involve substitution, insertion, deletion or larger chromosome changes.
Mutations create new alleles; they do not automatically cause disease or visible change.
Errors and mutagens can cause mutations
DNA-copying errors can occur spontaneously. Ionising radiation and some chemicals increase mutation rate by damaging DNA or interfering with replication.
Cells have repair systems, but some damage persists and becomes a mutation.
Inheritance depends on cell type
A mutation in a body (somatic) cell may affect that cell lineage, sometimes contributing to cancer, but is not normally passed to offspring.
A mutation in a gamete or its precursor can be inherited by offspring.
Mutation contexts
The same DNA change has different consequences in different cells.
| Location/type | Immediate effect | Inheritance potential |
|---|---|---|
| Somatic cell | Changes one body-cell lineage. | Usually not inherited. |
| Germline/gamete | Changes reproductive DNA. | Can be inherited. |
| Substitution | One base replaced. | May be silent/missense/nonsense. |
| Insertion/deletion | Base(s) added/removed. | May shift reading frame. |
| Chromosome change | Large DNA amount/arrangement altered. | Potentially broad effects. |
Language that earns precision
- mutation
- Change in DNA base sequence or chromosome structure/number.
- somatic mutation
- Mutation occurring in a non-reproductive body cell.
- germline mutation
- Mutation in a gamete or cell lineage producing gametes.
- mutagen
- Agent that increases mutation rate.
Common misconceptions
Claim: Mutations are always harmful.
Correction: They can be harmful, neutral or occasionally beneficial depending on context.
Claim: Mutation is the same as natural selection.
Correction: Mutation creates variants; selection changes reproductive success among variants.
Claim: Every body-cell mutation is inherited by children.
Correction: Only mutations in germline cells can usually be inherited.
Match the answer to the command word
Use “change in DNA base sequence”.
Identify whether the mutation is in a gamete-producing lineage.
Recall, apply, then justify
Define mutation and explain how it can create a new allele.
Hint
DNA sequence difference equals allele version.
Suggested marking points
- A mutation is a change in DNA base sequence.
- The changed sequence differs from the original gene sequence.
- It therefore forms a new allele version of that gene.
Distinguish somatic and germline mutations.
Hint
Body lineage versus reproductive lineage.
Suggested marking points
- Somatic mutations occur in body cells and are usually not inherited.
- Germline mutations occur in gametes/gamete precursors and can be inherited.
Explain why a mutation is necessary but not sufficient for evolution by natural selection.
Planning hint
New variant, inheritance, differential reproduction, frequency.
What a strong design includes
- Mutation creates a new allele/variation.
- The allele must be inherited to affect future generations.
- Individuals with different alleles may differ in survival or reproduction.
- Selection changes reproductive success in a particular environment.
- The allele frequency must increase or decrease across generations.
- A neutral mutation may persist without being selected.