Table 1.

Array-based comparative genomic hybridization versus single nucleotide polymorphism array

	aCGH	SNP-array
Probes	Traditionally, the probes are long oligonucleotides (50 to 70 bases) solely designed for copy number analysis. Newer platforms have added SNP-based probes for limited regions of the genome mainly to detect UPD (for example, Agilent CGH + SNP arrays)	SNP-based oligonucleotides designed for SNP genotyping. Copy number can be inferred by additional analysis. Newer platforms have added long oligonucleotides designed solely for copy number analysis to improve resolution (for example, Affymetrix SNP 6.0, Illumina 1M)
Experimentation	Genomic DNA from the patient and a control are labeled with different fluorophores and hybridized to the same array. The differences in signal intensity between the patient and control samples, which is converted to a log2 ratio, indicates a difference of copy number	In SNP-arrays the patient sample is hybridized to the microarray by itself. Copy number is determined by comparing the signal intensity data obtained from the patient sample with a collection of controls previously analyzed and incorporated into the analysis software
Resolution	Probes can be tiled to provide very high resolution. More flexibility and customization of probe content and density. Single exon resolution possible	The placement of probes is dependent on location of SNPs limiting resolution. Less flexibility in way of customization of probe content
Applications	Can only be used for copy number analysis. Will not detect UPD or consanguinity unless SNP probes are specifically added. Will also detect low-level mosaicism of CNVs	Will detect UPD, consanguinity, as well as copy number variations. Will also detect low-level mosaicism of CNVs

aCGH, array-based comparative genomic hybridization; CNV, copy number variation; SNP, single nucleotide polymorphism; SNP-array, SNP-based microarray; UPD, uniparental disomy.