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2.4 Recombination — Test 1
Q1. A drug that blocks DNA synthesis is LEAST likely to affect which process?✓ Photoreactivation
Q2. Site-specific recombination produces precise rearrangements at defined sequences. The key enzymes are:✓ Nuclease (recombinase) and ligase
Q3. BRCA-2 helps repair damaged DNA. Its loss of function impairs:✓ Repair by homologous recombination
Q4. Damage encountered at the replication fork (e.g. a gap opposite a lesion) is repaired by:✓ Recombination (post-replication) repair
Q5. During RecBCD-mediated homologous recombination in E. coli, what happens specifically AT the chi site?✓ Nuclease activity is modulated and a 3' single-strand tail is generated for RecA loading
Q6. Error-free repair of DNA double-strand breaks is accomplished by:✓ Homologous recombination
Q7. The Flp/FRT system is popularly used for:✓ Conditional (site-specific) gene manipulation/silencing
Q8. In the double-strand-break-repair (DSBR) model of homologous recombination, which combination of statements is correct? A) Triggered by a double-strand break. C) Strand invasion forms a displacement (D-)loop. E) Resolution can give crossover or non-crossover products.✓ A, C and E
Q9. The Holliday junction is an intermediate of:✓ Homologous DNA recombination
Q10. In which process does a DNA fragment from a dead bacterium enter a competent recipient and exchange for recipient DNA?✓ Transformation
Q11. Match the enzyme (Group II) to its role (Group I) and pick the correct order for I, II, III, IV:✓ 3,4,2,1
Q12. Horizontal gene transfer integrates incoming DNA mainly via:✓ Homologous recombination
Q13. Non-covalently linked DNA intermediates formed during homologous pairing are called:✓ Joint molecules
Q14. RecA-bound helical nucleoprotein filament forms through cooperative interaction with:✓ Single-strand binding protein (SSB)
Q15. The most important enzyme/protein in homologous recombination in E. coli is:✓ RecA
2.4 Recombination — Test 2
Q16. Which statement about RecA is WRONG?✓ It is an ATP-dependent nuclease that generates single-stranded DNA
Q17. Which is NOT required for RecA-dependent recombination between two DNA molecules?✓ Mismatch repair
Q18. The homologous-recombination repair pathway ('recombination repair') — which statement is INCORRECT?✓ The process is catalysed by topoisomerase II
Q19. The E. coli nuclease that initiates double-strand-break repair by homologous recombination is:✓ RecBCD (and resection nucleases)
Q20. UmuC, UmuD and RecA proteins are involved in:✓ SOS (translesion) repair
Q21. Which genetic element acts in cis for bacteriophage λ growth?✓ nut (N-utilization site)
Q22. Which yeast process moves a transposon by a replicative, RNA-mediated mechanism?✓ RNA-mediated (retrotransposition)
Q23. The transposase gene encodes an enzyme that:✓ Facilitates site-specific transposition/integration of the element
Q24. Polymerase β is the key polymerase of which repair pathway (relevant after recombination/excision)?✓ Base excision repair
Q25. For a single crossover, the frequency of recombinant gametes is HALF the frequency of crossing-over because:✓ Each crossover involves only two of the four chromatids of a bivalent
Q26. Defects in which enzyme pairs impair the post-proofreading repair pathways? A) Pol III + ligase, B) AP endonuclease + glycosidase, C) MutS + MutL, D) RecA + RecF.✓ B, C and D
Q27. Which protein binds single-stranded DNA to form the recombination filament and searches for homology?✓ RecA
Q28. RuvAB and RuvC in E. coli act respectively to:✓ Drive branch migration and resolve Holliday junctions
Q29. Gene conversion is best described as:✓ Non-reciprocal transfer of sequence from one allele to another
Q30. Site-specific recombination differs from homologous recombination in that it:✓ Acts at short defined recognition sequences without needing homology search