Q58 Match Group-I (selection agent) and Group-II (gene) in CORRECT combination.

Group-I	Group-II
P. Kanamycin	I. nptII
Q. Hygromycin	II. bar
R. Phosphinothricin	III. pat
S. Mannose	IV. ptxD
	V. hpt

The correct answer is option (C):
P – I (Kanamycin – nptII), Q – VI (Hygromycin – hpt), R – III (Phosphinothricin – bar), S – II (Mannose – pmi).

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Introduction

This article explains how to match Group-I (selection agent) and Group-II (gene) for a CSIR NET-style multiple choice question on plant genetic transformation. Correctly pairing antibiotic or herbicide selection markers such as kanamycin, hygromycin, phosphinothricin and mannose with their corresponding resistance or metabolic genes is essential for mastering plant biotechnology MCQs and understanding selection strategies in transgenic plants.

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Question breakdown

Group-I (selection agent)

• P. Kanamycin

• Q. Hygromycin

• R. Phosphinothricin

• S. Mannose

Group-II (gene)

• I. pmi

• II. bar

• III. nptII

• IV. ptxD

• V. dhfr

• VI. hpt

Task: Select the option that gives the correct combination of each selection agent with its corresponding gene.

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Correct matching explained

Kanamycin – nptII

• Kanamycin is an aminoglycoside antibiotic commonly used as a selection agent in plant and bacterial transformation.

• The nptII gene encodes neomycin phosphotransferase II, which inactivates kanamycin (as well as neomycin and G418) by phosphorylation, thereby conferring resistance.

So, P – III (Kanamycin – nptII) is the correct match.

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Hygromycin – hpt

• Hygromycin B is an aminoglycoside antibiotic widely used to select transformed plant and animal cells.

• The hpt (also called hph) gene encodes hygromycin phosphotransferase, which detoxifies hygromycin B and confers resistance.

Therefore, Q – VI (Hygromycin – hpt) is the correct pair.

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Phosphinothricin – bar

• Phosphinothricin (PPT) or glufosinate is a broad‑spectrum herbicide used as a selection agent in plant transformation.

• The bar gene encodes phosphinothricin acetyltransferase, which acetylates and inactivates phosphinothricin, giving herbicide resistance.

Thus, R – II (Phosphinothricin – bar) is correctly matched.

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Mannose – pmi

• In some plant transformation systems, positive selection uses mannose as a carbon source instead of antibiotics or herbicides.

• The pmi (phosphomannose isomerase) gene enables transformed cells to metabolize mannose by converting mannose‑6‑phosphate to fructose‑6‑phosphate, allowing only transformed cells to grow on mannose-containing medium.

Hence, S – I (Mannose – pmi) is the correct association.

Putting all together gives:

• P – III

• Q – VI

• R – II

• S – I

This combination corresponds to option (C).

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Why other options are incorrect

Option (A): P–III, Q–VI, R–II, S–I

• This option lists:

  • P–III (Kanamycin–nptII) ✔

  • Q–VI (Hygromycin–hpt) ✔

  • R–II (Phosphinothricin–bar) ✔

  • S–I (Mannose–pmi) ✔

• If any symbol or numbering in the printed question differs, conceptually all four pairs here are correct; any alternative that pairs these agents with other genes would be wrong for the reasons below.

(If the official key labels this as option (C) instead of (A), follow the official code; conceptually, the correct mapping is the one containing all four correct pairs above.)

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Why other genes do not match these agents

• ptxD (IV): Encodes phosphite dehydrogenase, used for selection on phosphite, not on kanamycin, hygromycin, phosphinothricin or mannose.

• dhfr (V): Encodes dihydrofolate reductase; mutant versions provide resistance to antifolates like methotrexate or trimethoprim, not to the agents listed in Group-I.

Any option that pairs kanamycin, hygromycin, phosphinothricin or mannose with ptxD or dhfr is therefore incorrect.

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Summary table of correct pairs