Reporter Enzymes in Genetic Transformation — NEET Biology

Correct answer: C — S2, S3 and S4 only

The core concept involves the features and properties of cloning vectors. S1: Incorrect. NCERT states, "Bacteriophages because of their high number per cell, have very high copy numbers of their genome within the bacterial cells. Some plasmids may have only one or two copies per cell whereas others may have 15-100 copies per cell. Their numbers can go even higher." While both can achieve high copy numbers, plasmids are not *always* preferred, and bacteriophages are also known for very high copy numbers. S2: Correct. NCERT states, "This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA." S3: Correct. NCERT states, "In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non- transformants and selectively permitting the growth of the transformants." S4: Correct. For efficient cloning, a vector ideally has "very few, preferably single, recognition sites for the commonly used restriction enzymes." (Page 169). pBR322 (Figure 9.4) has single recognition sites for various enzymes (e.g., BamH I in tetR gene, Pst I in ampR gene), which allows for precise insertion without unintended fragmentation. S5: Incorrect. NCERT states, "The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation... and the colonies do not produce any colour, these are identified as recombinant colonies." So, blue colonies indicate *non-recombinants*, not insertional inactivation. Based on the analysis, S2, S3, and S4 are the correct statements. Option A is incorrect because S1 and S5 are not correct. Option B is incorrect because S4 is also correct. Option C is correct as S2, S3, and S4 are the correct statements. Option D is incorrect because S1 and S5 are not correct. This question evaluates the knowledge of essential vector features, their functions, and selection methods.