Selectable Markers in Vectors — NEET Biology
✅ Asked in NEET 2026Selectable marker: 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. Transformation is a procedure through which a piece of DNA is introduced in a host bacterium (you will study the process in subsequent section). Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli. The normal E. coli cells do not carry resistance against any of these antibiotics.
NTA tests whether students understand why selectable markers (like ampicillin resistance genes) are essential in recombinant DNA vectors. The core concept: these markers help distinguish transformed bacteria from non-transformed ones. The common trap: students confuse selectable markers with the ori (origin of replication)—both are needed, but they serve different purposes. Ori enables replication; markers enable selection. Remember: when bacteria are exposed to antibiotics, only transformed cells carrying the resistance gene survive and grow. This is how scientists isolate successful transformants. NEET frequently asks which genes work as markers or why a specific antibiotic resistance gene is used in E. coli—so know that E. coli naturally lacks resistance to ampicillin, tetracycline, and kanamycin.
This paragraph was tested 4 times in NEET.
Insertion of foreign DNA at the BamHI site in pBR322 results in the loss of antibiotic resistance towards:
Given below are two statements: Statement I: The selectable marker helps in identifying the recombinant from the non-recombinant. Statement II: Ampicillin resistance gene can be used as a selectable marker. In light of the above statements, choose the most appropriate answer: (NEET 2025)
Which of the following is not a selectable marker of cloning vectors? (NEET 2024)
A gene whose expression helps to identify transformed cell is known as: (NEET 2017)
Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.