Which of the following genes is most frequently used as a selectable marker in $E . co l i$ cloning vectors?

easy MCQ 1 mark Class 12 · Biology · Biotechnology Principles and Processes

Answer

bla (

β

-lactamase) conferring ampicillin resistance

The correct answer is bla ( $β$ -lactamase) conferring ampicillin resistance — Therefore the correct choice is the $b l a$ gene.

Step-by-step solution

Identify the purpose of a selectable marker: it allows growth of only those bacteria that have taken up the vector.
Recall the most common antibiotic used for selection in basic cloning experiments is ampicillin.
The gene that provides resistance to ampicillin is the $b l a$ gene encoding $β$ -lactamase.
Compare with other options: $n eo$ gives kanamycin resistance, $h p h$ gives hygromycin resistance, $d h f r$ gives trimethoprim resistance; these are less commonly used in routine cloning.
Therefore the correct choice is the $b l a$ gene.

Common mistake: Confusing the antibiotic resistance gene with less common markers like neo or hph

Concept tested: Selectable marker in bacterial vectors