6.6 Mutations and genetic variants
5 exam questions worth 10 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is a mutation?
Mark scheme
a change in the (base sequence of) DNA
Model answer
A mutation is a change in the base sequence of DNA.
Explain why most mutations have no effect on an organism.
Mark scheme
Any two from:
- happen in non-coding DNA (1)
- the new triplet codes for the same amino acid (1)
- the protein still folds / has the same shape (1)
Model answer
Many happen in DNA that does not code for a protein, and others change the amino acid sequence so little that the protein still folds into the same shape.
Explain how a mutation in the gene for an enzyme could stop the enzyme working.
Mark scheme
- change in the base sequence (1)
- changes the amino acid sequence (1)
- protein folds differently / changes shape (1)
- active site changes so substrate no longer fits (1)
Model answer
The mutation changes the base sequence, so a different amino acid is coded for. The chain folds differently, so the enzyme's shape changes. The active site no longer fits the substrate, so the enzyme cannot work.
A mutation happens in non-coding DNA. Suggest how it could still affect the phenotype.
Mark scheme
- non-coding DNA can switch genes on / off (1)
- so a gene may not be expressed / protein not made (1)
Model answer
Non-coding DNA can switch genes on and off, so the mutation might stop a gene being expressed, and the protein would not be made.
Which statement about genetic variants is correct?
Choose one answer.
Correct Not quite: the answer is Most variants have no effect on the phenotype
Mark scheme
C
Model answer
C: most genetic variants have no effect on the phenotype.
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