The big idea: Mutations are random: they can happen anywhere in the genome, and nothing aims them at a useful trait.
The points to remember
- A mutation can occur anywhere in the base sequence of a genome.
- Where and when a mutation happens cannot be predicted.
- Some bases have a higher probability of mutating than others.
- No natural mechanism makes a deliberate change to a particular base to change a trait.
- Mutagens raise the rate of mutation, but not its direction.
Remember it as: Anywhere, any time, never on purpose.
Real example: C next to G. In human DNA, a cytosine that is followed by a guanine mutates far more often than most other bases. Mutations are random, but not equally likely at every base.
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What 'random' means: Random means unpredictable and not aimed, not 'equally likely everywhere'.
True of mutations
- Can happen anywhere in the genome
- Cannot be predicted
- Some bases mutate more often
- Rate raised by mutagens
Not true of mutations
- Happen only in certain genes
- Happen because the organism needs them
- Are aimed at a useful trait
- Only happen in germ cells
Need does not cause mutation: Bacteria do not mutate because an antibiotic is present. Resistant mutants arise by chance; the antibiotic then selects them.
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How it is asked: A 1A item asking for a true general feature of mutations: they occur randomly.
IB-style questionOutline[2 marks]
Outline what is meant by saying that mutations are random.
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See the answer broken into clear points, with guidance on how each point earns marks.