Quick revision: every question with its correct answer. For the full explanation, open the relevant test and tap View Solution.
CSIR-NET Challenge
Q1. Random yeast DNA fragments were cloned into a bacterial plasmid carrying gene 'X' (essential for yeast viability on minimal media), and used to transform a recombination-deficient yeast strain lacking 'X'. Transformants that survive on minimal media must essentially contain:✓ A yeast autonomously replicating sequence (ARS)
Q2. In bacteria, fMet is the first amino acid, yet not all mature proteins keep a formyl group or an N-terminal Met. Which statements explain this? A. Deformylase removes the formyl group during/after synthesis. B. Aminopeptidase removes only the N-terminal Met. C. Aminopeptidase removes the N-terminal Met plus one or two further residues.✓ A and C
Q3. Match: I. Transduction, II. Transformation, III. Transfection, IV. Transvection — with the descriptions 3. Uptake of free DNA into bacteria; 4. Introducing DNA into bacteria via a virus; 5. Introducing DNA into mammalian cells; 2. Interaction between alleles on homologous chromosomes (transvection). The correct matching is:✓ I-4, II-3, III-5, IV-2
Q4. A genomic-library clone is screened by probe hybridization, after which a stringent wash is applied. Which statements correctly describe the stringent wash? A. It removes unincorporated and non-specifically hybridized probe. C. It uses low salt and a higher temperature. D. Salt shields the phosphate charge so genuine perfectly-matched hybrids stay intact.✓ A, C and D
Q5. In knockout-mouse production, the targeting DNA carries neo (G-418 resistance, inside the homology region) and tk-HSV (ganciclovir sensitivity, outside the homology region), with neo disrupting the target gene. Considering BOTH homologous and random (non-homologous) integration, which statement is INCORRECT?✓ Homologous recombinants are killed by ganciclovir
Q6. Hormone induces gene X via two proteins, Let1 and Let2. Expression of gene X was scored in lines over-expressing (OE) or knocking out (KO) each protein and their combinations, in the presence of hormone. Epistasis analysis of these results best fits which signalling order?✓ Hormone → Let1 → Let2 → Gene X
Q7. To catalogue genes expressed at a developmental stage, mRNAs were reverse-transcribed, cloned and sequenced. A few cDNA sequences had NO match in the genomic DNA, were U-rich, and occurred in dispersed stretches. The most likely explanations are: C. Trans-splicing; D. Guide-RNA-directed U-insertion editing (endonuclease + terminal-U-transferase + RNA ligase); E. C→U deamination editing.✓ C, D and E
Q8. Cloning YFG (0.5 kb) into vector pE (3 kb) at a single BamHI site, with a target 1:3 vector:insert MOLAR ratio. If 100 ng of vector is used, the mass of insert required is approximately:✓ 50 ng
Q9. A researcher could clone gene Y easily but never gene X alone; however, X cloned readily into a plasmid that already carried Y. Which statements explain this? A. The Y product is not lethal to the cell. C. The X product is toxic/lethal to the cell. D. The Y product inhibits or neutralizes the X product.✓ A, C and D
Q10. A T0 transgenic plant carrying a herbicide-resistance transgene shows TWO bands on a Southern blot (probe internal to the digestion sites) but its selfed T1 progeny segregate 3:1 (resistant:sensitive). The correct interpretation is:✓ A double-copy event with the two copies tightly linked (segregating as a single locus)
Q11. A 4.8 kb plasmid gives these digests (each single enzyme linearizes it): E1+E2 = 0.5 + 4.3 kb; E2+E3 = 0.4 + 4.4 kb; E3+E4 = 2.0 + 2.8 kb; E1+E4 = 1.9 + 2.9 kb. Which statement is correct?✓ E2 lies between E1 and E3 on the map
Q12. A PCR fragment is to be cloned into a vector cut with XhoI (C^TCGAG) and SmaI (CCC^GGG). Which pair of enzyme sites, engineered into the PCR primers, would create COMPATIBLE ends for this cloning?✓ SalI (G^TCGAC) and EcoRV (GAT^ATC)
Q13. Which statements about determining a gene’s position are correct? I. DNA FISH locates a gene in the nucleus. II. RNA FISH with an exonic probe can report gene position. IV. CRISPR (dCas9) imaging locates a gene in LIVE cells.✓ I, II and IV
Q14. An insert is flanked by BamHI on one side (5′ overhang) and KpnI on the other (3′ overhang). It must go into a plasmid that has only a unique, blunt EcoRV site. The correct multi-step strategy is to:✓ Digest the insert with both BamHI and KpnI, blunt both ends with Klenow (fill-in the 5′ overhang and resect the 3′ overhang), then ligate into the EcoRV-cut plasmid
Q15. Expression of gene 'A' is regulated by Mg²⁺. Gene A was analysed by Northern hybridization (N, mRNA level) and Western blotting (W, protein level) in untreated (UN) vs Mg²⁺-treated (T) cells, and in a mutant carrying a 6-bp deletion in the transcript’s 5′UTR. If regulation of gene A is ONLY at the level of translation, the expected experimental profile is one in which:✓ The Northern (mRNA) signal stays constant while the Western (protein) signal changes with treatment