In a typical microarray experiment, RNA is extracted from both cancerous and normal cells. The RNA is then converted into complementary DNA (cDNA) and labeled with fluorescent dyes. These labeled cDNAs are hybridized to the microarray, where they bind to complementary DNA sequences on the array. The level of fluorescence measured at each spot indicates the expression level of the corresponding gene, allowing researchers to compare gene expression between cancerous and normal cells.
