Designing gene probes — essential properties for practical use For a DNA or RNA gene probe to be useful in detecting a specific target sequence, which requirements must it meet?

Introduction / Context:
Nucleic acid probes are short, complementary sequences used to find specific DNA/RNA targets in blots, in situ assays, or diagnostic tests. Their effectiveness hinges on specificity and detectability. This question tests your grasp of probe design fundamentals that ensure selective hybridization and robust signal detection.

Given Data / Assumptions:

• A probe must bind only to its intended target sequence under chosen stringency conditions.
• Detection requires a label that can be visualized or quantified.
• Probe length and composition (GC content, melting temperature) influence performance.

Concept / Approach:

Specificity comes from sequence uniqueness and appropriate length; too short increases cross-hybridization, too long can hinder penetration and kinetics. Labels (e.g., 32P, digoxigenin, biotin, fluorescent dyes) enable autoradiography or imaging. Both properties—distinct sequence content and detectable labeling—are mandatory for practical probe applications, whether in Southern/Northern blots or in situ hybridization.

Step-by-Step Solution:

Verification / Alternative check:

Pilot hybridizations showing strong signal at the target band/region with negligible background confirm that both criteria are met.

Why Other Options Are Wrong:

Either criterion alone is insufficient: unlabeled probes are undetectable; labeled but non-specific probes cause false positives. Circularization (E) is unnecessary for hybridization-based detection.

Common Pitfalls:

Neglecting GC content and Tm matching to wash conditions; failing to include controls for background binding.

Final Answer:

Both (a) and (b)