Practice question

Comparative Genomic Hybridization assesses DNA copy number imbalances by competitive hybridization. Genomic DNA from test sample, for instance tumor tissue, is labeled with green fluorochrome, while reference normal genomic DNA is labeled with red fluorochrome. Equal amounts are co-hybridized onto normal metaphase chromosomes or microarray probes. Ratio of green to red fluorescence along chromosomes indicates gains shown by green predominance or losses shown by red predominance. Use of only one labeled population or RNA probes would eliminate competitive quantitative principle fundamental to detecting deletions and amplifications.