In gene expression microarray, the probe used to
assess the amount of mRNA can be either
complementary DNA (cDNA) or an
oligonucleotide. The probe is amplified by
polymerase chain reaction (PCR) and spotted onto
an array which is then immobilised on a solid
support (glass slide).16 In the experiment RNA is
extracted from the samples and, by the process of
reverse transcription and addition of fluorescent
dyes, labelled cDNA is formed (both
normal/control and diseased/case) which is then
combined and hybridised with the microarray
slide. These microarray glass slides are often called
chips. The amount of the two dyes is representative
of the gene expression in the different samples. An
ultraviolet laser is used to scan the slide which
detects the amount of fluorescent signal for each
gene. This image is then analysed