DNA microarrays allow for the rapid analysis of gene expression across thousands of genes. There are two main technologies used - Affymetrix chips using single-stranded DNA oligonucleotides and Stanford chips using PCR products. The process involves isolating mRNA, creating fluorescently labelled cDNA, hybridizing it to probes on a microarray plate, scanning with a laser to detect fluorescence, and analyzing the data to determine which genes are expressed or not expressed in samples. DNA microarrays have applications in gene discovery, disease diagnosis by analyzing gene expression patterns in tumors, studying drug responses, and researching the effects of toxins on cells.