DNA genotyping and sequencing. Close-up of a technician washing arrays used in genome-wide association studies (GWAS). These studies search the genome for small variations, called single nucleotide polymorphisms or SNPs, that occur more frequently in people with a particular disease than in people without the disease. This research is taking place at the Cancer Genomics Research Laboratory, in Gaithersburg, Maryland, USA, part of the National Cancer Institute's Division of Cancer Epidemiology and Genetics (DCEG). Photographed in 2016.