Question

An example for a scorable marker in Genetic engineering

• A. hpt
• B. gus
• C. amp
• D. nptII

Hint:

Selectable markers (like hpt, amp, nptII) allow transgenic cells to survive on selective media, whereas scorable markers (like gus or gfp) produce a visible phenotypic signal.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Genetic transformation protocols use two types of marker genes to identify transgenic tissues:
1. Selectable markers: Genes that confer resistance to selective agents (like antibiotics or herbicides), allowing only transgenic cells to survive on selective media.
2. Scorable markers (or reporter genes): Genes that encode an enzyme with a detectable activity, producing a visible color or fluorescent signal to identify transgenic tissue without killing non-transgenic cells.

Step 2: Detailed Explanation:
Let us analyze each marker gene listed in the options:
- The gus gene (B) encodes the enzyme \(\beta\)-glucuronidase.
When transgenic plant tissues expressing the gus gene are incubated with the substrate X-gluc (5-bromo-4-chloro-3-indolyl glucuronide), the enzyme cleaves the substrate to produce a distinct blue precipitate.
This histochemical assay allows researchers to easily score and quantify transgene expression, making gus a classic scorable marker.
- The hpt gene (A) confers resistance to the antibiotic hygromycin, acting as a selectable marker.
- The amp gene (C) confers resistance to ampicillin, acting as a selectable marker.
- The nptII gene (D) encodes neomycin phosphotransferase II, which confers resistance to kanamycin, acting as a selectable marker.

Step 3: Final Answer:
Therefore, the scorable marker among the options is the gus gene, corresponding to option (B).