Practice question

A DNA microarray contains ordered microscopic spots, each printed with multiple identical probes complementary to a single transcriptional unit. Typically, probes correspond to a specific gene, EST, or predicted open reading frame. When fluorescently labeled cDNA or cRNA derived from samples hybridizes, intensity at each coordinate correlates with abundance of that gene's transcripts. Although a gene may contain multiple exons, array design aggregates exons under one gene identifier or multiple spots per exon in exon arrays. Spots do not represent individual primers, proteins, or isolated exons in conventional expression arrays.