SNP50 BeadChip (black, lower center) is used to detect single nucleotide polymorphisms (SNPs) in an organism's genetic sequence. Close-up images of the beads on the chip can be seen in the background. SNPs are single nucleotide variations in a DNA (deoxyribonucleic acid) sequence. For a variation to be an SNP it must occur in at least 1% of the population. Each chip has the capability of testing just under 80 million DNA-coated glass beads, allowing the Agricultural Research Service (ARS), the USDA's principal research agency, to test 60,000 genetic locations at once.