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Introduction to Gene Mutation Quiz
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Which type of mutation changes the DNA sequence but does not alter the amino acid sequence of the encoded protein, because of redundancy in the genetic code?
- A Synonymous mutation You picked ✓
- B Non-conservative missense mutation You picked ✕
- C Nonsense mutation You picked ✕
- D Germ-line mutation You picked ✕
- E Conservative missense mutation You picked ✕
Correct!
Incorrect
The answer is A: Synonymous mutation
Explanation
Why A is correct
See Types of Mutations. Option A is correct. The genetic code is read in triplets of bases called codons, and there are 64 possible codons but only 20 amino acids, so most amino acids are specified by more than one codon. This built-in backup is called redundancy (the code is said to be degenerate). A single-base change that turns one codon into another codon for the same amino acid is a synonymous or silent mutation: the DNA sequence has changed, but the amino acid sequence of the protein has not. These changes often occur in the third base of a codon. The other point mutations all alter the protein in some way: a missense mutation substitutes a different amino acid, and a nonsense mutation introduces a premature stop codon. Missense mutations are subdivided into conservative (the new amino acid has similar chemical properties) and non-conservative (the new amino acid has different properties). The memory aid is: silent = same amino acid; missense = mistaken amino acid; nonsense = stop.
- Redundancy: 64 codons but only 20 amino acids, so most amino acids have several codons.
- Synonymous (silent): the DNA changes but the amino acid sequence stays the same.
- Other point mutations: missense swaps one amino acid, nonsense creates a premature stop codon.
Why the other options are incorrect
- B. Non-conservative missense mutation: A non-conservative missense mutation changes the amino acid to one with different chemical properties. The amino acid sequence is altered, and the effect on the protein can be significant. Your answer
- C. Nonsense mutation: A nonsense mutation creates a premature stop codon, so translation ends early and the protein is shortened. This changes the protein sequence rather than leaving it intact. Your answer
- D. Germ-line mutation: Germ-line mutation describes where a mutation occurs (in an egg or sperm cell and so can be inherited), not what it does to the amino acid sequence. A germ-line mutation can be silent, missense or nonsense. Your answer
- E. Conservative missense mutation: A conservative missense mutation does change the amino acid, to one with similar chemical properties. The protein sequence therefore does change, even if the effect may be small. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which chromosomal mutation involves fusion of the long arms of two acrocentric chromosomes following loss of their short arms?
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2
A researcher is studying mechanisms by which mutations can arise within human cells. Which process represents an endogenous cause of mutation that can directly inactivate a gene by inserting itself into a new genomic location?
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