GeneChip microarrays consist of small DNA fragments (referred to here as probes), chemically synthesized at specific locations on a coated quartz surface. The precise location where each probe is synthesized is called a feature, and millions of features can be contained on one array. By extracting and labeling nucleic acids from experimental samples, and then hybridizing those prepared samples to the array, the amount of label can be monitored at each feature, enabling a wide range of applications on a whole-genome scale — including gene- and exon-level expression analysis, novel transcript discovery, genotyping, and resequencing. Microarray analysis can also be combined with chromatin immunoprecipitation to perform genome-wide identification of transcription factors and their respective binding sites.