Question

Consider the following statements. Assertion (A): E. coli having pBR322 with DNA insert at BamHI site cannot grow in medium containing tetracycline. Reason (R): Recognition site for BamHI is present in the \(\mathrm{tet}^R\) region of pBR322.

• A. Both (A) and (R) are true, (R) is the correct explanation of (A)
• B. Both (A) and (R) are true, (R) is not the correct explanation of (A)
• C. (A) is true, but (R) is false
• D. (A) is false, but (R) is true

Hint:

In pBR322, \[ \boxed{ \begin{aligned} &\text{BamHI site} &&\rightarrow \mathrm{tet}^R\text{ gene} &\text{PstI site} &&\rightarrow \mathrm{amp}^R\text{ gene} \end{aligned} } \] Insertion of foreign DNA into these sites causes insertional inactivation of the corresponding antibiotic resistance gene.

Answer 1

The Correct Option is A

Step 1: Recall the BamHI site in pBR322. The restriction site for BamHI lies within the \[ \boxed{\mathrm{tet}^R\text{ (tetracycline resistance) gene}.} \] Insertion of foreign DNA at this site causes insertional inactivation of the tetracycline resistance gene.

Step 2: Evaluate the assertion. Since the \(\mathrm{tet}^R\) gene is disrupted, \[ \boxed{\textit{E. coli} containing the recombinant plasmid cannot grow on tetracycline-containing medium.} \] Thus, the assertion is true.

Step 3: Evaluate the reason. The reason correctly explains why the recombinant bacteria lose tetracycline resistance. Hence, \[ \boxed{\text{Both (A) and (R) are true, and (R) is the correct explanation of (A).}} \] Therefore, the correct option is \[ \boxed{(A).} \]