A novel suspension hybridization
assay was used to determine
nucleic acid copy number by
flow cytometry. The
assay was validated with low copy (lc) products
ranging in length from 100 to 2304 bp conjugated to spectrally-distinct
polystyrene microspheres. In the example provided herein, these conjugated microspheres were used as
multiplex hybridization probes to detect
homologous sequences in
genomic DNA extracted from cytogenetic
cell pellets and labeled with
biotin-dUTP. Hybridization was detected with
phycoerythrin-labeled
streptavidin and analyzed by
flow cytometry. Copy number differences were distinguishable by comparing the mean
fluorescence intensities of test probes with a diploid reference probe in
genomic DNA of patient samples and
abnormal cell lines. The
assay is capable of distinguishing a single
allele and three alleles at a test locus from a biallelic reference sequence, regardless of chromosomal context. The assay is an improvement on previous methods which require prior amplification of locus-specific target
DNA because, lc probes provide adequate specificity and sensitivity for accurate copy number determination of homologous targets. Because of its high sensitivity and accuracy, the assay is useful for determination of
nucleic acid copy number for a variety of applications, including determination of genomic copy number in humans, animal models of
disease and in solution, measurement of transcript levels,
forensic DNA analysis, and
quality control analysis in
agriculture.