BACs are Bacterial Artificial Chromosomes, large cloned sequences of human DNA typically 170,000 bases long. BAC probes have long been used for FISH. The BACs-on-Beads® technology uses probes generated from selected BACs immobilized onto Luminex® xMAP® encoded beads. The resulting bead sets are used to assay chromosomal gains and losses from minute sample amounts with high throughput. BACs-on-Beads analysis comprises hybridization of DNA sample sequences to BAC-derived probes representing the identified target regions. Samples are enzymatically labeled with biotin, and after hybridization in a 96-well plate a fluorescent streptavidin-phycoerythrin reporter is bound to the biotin label. Male and female reference DNA is also hybridized and the fluorescence ratio between each sample and reference DNA are compared to provide a clear display of any copy number changes in the targeted regions.