Which mutant most likely results in a frameshift?

Answer: D Mutant D inserts an extra base (A) after AAA, shifting the downstream reading frame. Mutant A is silent/missense, B is nonsense (premature stop), C is a single-base substitution that does not change frame.

Answer: Changes a codon to a stop codon, truncating the protein Truncated proteins are usually nonfunctional and rapidly degraded.

UV light typically causes

Answer: Pyrimidine dimers (e.g., thymine-thymine), which distort DNA and require repair UV damage forms covalent bonds between adjacent thymines, blocking replication unless repaired by NER (nucleotide excision repair).

AP Biology · Topic 6.7

Mutations Practice

Part of Gene Expression and Regulation.(IST-2.C)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$Which mutant most likely results in a frameshift?$
- A
  $A$
- B
  $D$
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- C
  $B$
- D
  $C$
Why
$Mutant D inserts an extra base (A) after AAA, shifting the downstream reading frame. Mutant A is silent/missense, B is nonsense (premature stop), C is a single-base substitution that does not change frame.$
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Sample 2difficulty 2/5
$A nonsense mutation$
- A
  $Changes a codon so it encodes a different amino acid$
- B
  $Inserts a base, shifting the reading frame for all downstream codons$
- C
  $Changes a codon to a synonymous one, leaving protein unchanged$
- D
  $Changes a codon to a stop codon, truncating the protein$
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Why
$Truncated proteins are usually nonfunctional and rapidly degraded.$
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Sample 3difficulty 2/5
$UV light typically causes$
- A
  $Frameshift insertions (e.g., extra bases), which shift reading frames and require repair$
- B
  $Double-strand breaks (e.g., chromosome fragments), which separate DNA and require repair$
- C
  $Pyrimidine dimers (e.g., thymine-thymine), which distort DNA and require repair$
  check_circle
- D
  $Single base substitutions (e.g., G-to-A), which alter codons and require repair$
Why
$UV damage forms covalent bonds between adjacent thymines, blocking replication unless repaired by NER (nucleotide excision repair).$
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Sample 4difficulty 2/5
$A silent mutation$
- A
  $Changes a single nucleotide but, due to code redundancy, leaves the encoded amino acid unchanged$
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- B
  $Changes a single nucleotide and creates a premature stop codon, truncating the protein$
- C
  $Inserts a single nucleotide and shifts the reading frame for all downstream codons$
- D
  $Changes a single nucleotide and substitutes one amino acid for another in the protein$
Why
$Point mutation in a degenerate position has no effect on the protein sequence.$
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Sample 5difficulty 2/5
$A missense mutation$
- A
  $Changes one nucleotide so the codon still encodes the same amino acid$
- B
  $Changes one nucleotide so the codon becomes a premature stop signal$
- C
  $Deletes one nucleotide, shifting the reading frame for downstream codons$
- D
  $Changes one nucleotide so the codon encodes a different amino acid$
  check_circle
Why
$Sickle-cell anemia is caused by a missense mutation: glutamic acid \to valine at position 6 of β-globin.$
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