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4.6 Mutations: Suppressors, Mutagens & Detection — Test 3
Q1. A point mutation involving the addition or deletion of a single base pair is termed a:✓ Frameshift mutation
Q2. Acridine dyes (e.g. acridine orange) typically induce which kind of mutation?✓ Frameshift (insertion/deletion)
Q3. 5-Bromouracil most commonly induces which base-pair change?✓ T:A to C:G
Q4. 2-Aminopurine induces mutation by:✓ A base-pair change (transition)
Q5. Which mutagen is most likely to produce a single amino-acid change in a protein?✓ Ethyl methanesulfonate (EMS)
Q6. Spontaneous deamination of 5-methylcytosine produces:✓ Thymine
Q7. A mutation that changes a codon but does not change the encoded amino acid or protein function is a:✓ Silent mutation
Q8. Which situation represents intergenic suppression of a coding-sequence mutation?✓ An amber (stop) codon recognised by the altered anticodon of a tRNA
Q9. A tRNA gene mutated in its anticodon so it can read a nonsense codon is called a:✓ Nonsense suppressor
Q10. The 'spontaneity' of a mutation means it:✓ Occurs in the absence of any exogenous mutagen
Q11. To study the function of a gene that is essential (its loss is lethal), the most useful mutants are:✓ Temperature-sensitive (conditional) mutants
Q12. An aspartate (GAU/GAC) is changed to alanine (GCx), and reversion is possible only via reactive oxygen species. This original mutation is a:✓ Transversion
Q13. In a bacterial operon with structural genes A-B-C (in that order), a polar mutation in gene B reduces expression of:✓ Genes B and C
Q14. In the lac operon, a nonsense mutation in lacZ that lowers expression of the downstream permease and transacetylase genes is explained by:✓ A polar effect of the mutation
Q15. The Ames test for mutagenicity classically uses:✓ Auxotrophic (his⁻) Salmonella plus a liver extract
Q16. To distinguish true reversion (at the original site) from suppression (a second-site mutation), one can use:✓ Recombination (a genetic cross)
Q17. 2-Aminopurine pairs normally with thymine but occasionally with cytosine, producing:✓ A transition
Q18. Mutagen X is reverted by base analogs and hydroxylamine but not by acridine; mutagen Y is reverted only by acridine. This indicates:✓ X causes base substitutions (e.g. transitions); Y causes insertions/deletions
Q19. In which disorder do unaffected parents or grandparents carry a 'premutation' that can expand in later generations?✓ Fragile-X syndrome
Q20. Match each mutagen with its mechanism and select the correct option.✓ A-ii, B-iv, C-i, D-iii