Gene expression profiling tools: What is the term for the small solid supports onto which hundreds of thousands of tiny DNA spots are printed to screen gene expression across many genes at once?

Introduction / Context:
Before high-throughput RNA sequencing became common, gene expression across thousands of genes was profiled using planar substrates covered with many DNA probes. Recognizing the correct term for these supports is foundational in genomics history and methods.

Given Data / Assumptions:

• Small solid supports (slides or chips) with many DNA spots.
• Purpose: screen gene expression or detect specific sequences.
• We must distinguish from classic blotting techniques and libraries.

Concept / Approach:

DNA microarrays (gene chips) contain immobilized oligonucleotides or cDNAs that hybridize with labeled targets (e.g., cRNA or cDNA) from samples. Fluorescent readouts quantify expression differences across conditions, tissues, or time points.

Step-by-Step Solution:

Verification / Alternative check:

Historically, microarrays have been used for differential expression, SNP genotyping, and copy-number variation; this matches the description.

Why Other Options Are Wrong:

Southern blot: DNA detection on membranes after electrophoresis; not a high-density array.

Northern blot: RNA detection technique.

Cloning library: collection of cloned DNA fragments; not a spotted array.

Common Pitfalls:

Confusing blotting (gel-based) with array (surface probe-based) techniques; assuming all hybridization methods are interchangeable.

Final Answer:

DNA microarrays