40. Which of the following techniques is NOT applicable for evaluating the expression of a
transgene?
(A) Northern blot
(B) RT-PCR
(C) Western blot
(D) Southern blot

Which Technique Is Not Used for Transgene Expression Analysis?

Southern blot does not evaluate transgene expression, as it detects DNA integration rather than RNA or protein levels. The correct answer is (D) Southern blot.

Correct Answer

(D) Southern blot​

Overview

Transgenes are foreign genes introduced into organisms, often studied in plant biology and genetics to confirm expression at RNA or protein levels. Techniques like Northern blot, RT-PCR, and Western blot measure transcription or translation directly. Southern blot, however, only confirms DNA presence and copy number, not active expression.​

Option Breakdown

Northern Blot (A)

Detects specific RNA transcripts from the transgene by size-separating total RNA, transferring to a membrane, and hybridizing with a labeled probe. Used to assess mRNA abundance, size, and splicing in gene expression studies.​

RT-PCR (B)

Reverse transcribes transgene mRNA to cDNA, then amplifies via PCR for quantification, often quantitative (qRT-PCR). Highly sensitive for low-expression transgenes in tissues like plants.​

Western Blot (C)

Separates transgene-encoded proteins by electrophoresis, transfers to a membrane, and detects with antibodies. Measures translation and protein levels, confirming functional expression.​

Southern Blot (D) – Not Applicable

Digests genomic DNA with restriction enzymes, separates fragments, and probes for transgene integration sites or copy number. Cannot detect RNA or protein, so unsuitable for expression evaluation.​