Practice question

Traditional chromosomal CGH hybridizes differentially labeled genomic DNAs onto normal metaphase spreads, limiting resolution to approximately 5 to 10 megabases because chromosome condensation and optical resolution constrain breakpoint mapping. Microarray CGH, also called array CGH, hybridizes same competitive probe mixture onto thousands of mapped BAC clones, cDNA, or oligonucleotide probes immobilized on glass slides. Since probe genomic coordinates are precisely known and spots are non-overlapping, resolution improves to kilobase level, enabling detection of microdeletions and microduplications invisible on metaphase chromosomes, unlike limitations inherent to PCR, northern blot, or RPA.