Traditional gene expression microarray schematic Traditional gene expression microarray schematic. DNA oligonucleotide probes are first generated utilizing DNA cloning techniques. These probes are then printed onto a substrate (eg, glass), placing hundreds to millions of microspots on one slide with each microspot composed of the same probe. In this figure, RNA is extracted from the patient sample and a reverse transcription PCR reaction produces amplified cDNA. The figure represents a traditional CGH microarray, so reference RNA is also reverse transcribed and amplified to produce reference cDNA. The cDNA's from the patient and reference are differentially labeled with fluorophores that emit light at different excitation wavelengths and allowed to hybridize to the microarray slide. The slide is washed to remove excess unbound fluorescently labeled cDNA. The slide is then visualized with the two different excitation wavelengths of the fluorophores. The two images are merged and compared by a computer for the intensities of each fluorophore at each microspot. The green spots in this image represent decreased expression in the test sample, the red spots represent increased expression in the test sample, and the yellow spots represent a level of expression similar to the reference sample. In some microarrays, the reference DNA intensities are stored digitally and not physically added to the slide. In these set-ups with digital references, patient samples are hybridized, the fluorescent intensities of the microspots are examined, and the intensities are compared to the digital reference. Reprinted with permission from Willey JM, Sherwood LM, Woolverton CJ. Prescott's Microbiology, 8th ed. Figure 16.12. Source: MOLECULAR DIAGNOSTIC TESTING, Pediatric Laboratory Medicine Citation: Jones PM, Dietzen DJ, Haymond S, Bennett MJ. Pediatric Laboratory Medicine; 2017 Available at: http://accesspediatrics.mhmedical.com/DownloadImage.aspx?image=/data/books/2219/jonesped_ch13_f005-1.png&sec=171097266&BookID=2219&ChapterSecID=171097221&imagename= Accessed: October 22, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved