A main disadvantage of conventional CGH is its inability to detect structural chromosomal aberrations without copy number changes, such as mosaicism, balanced chromosomal translocations, and inversions. CGH can also only detect gains and losses relative to the ploidy level. In addition, chromosomal regions with short repetitive DNA sequences are highly variable between individuals and can interfere with CGH analysis. Therefore, repetitive DNA regions like centromeres and telomeres need to be blocked with unlabeled repetitive DNA (e.g. Cot1 DNA) and/or can be omitted from screening. Furthermore, the resolution of conventional CGH is a major practical problem that limits its clinical applications. Although CGH has proven to be a useful and reliable technique in the research and diagnostics of both cancer and human genetic disorders, the applications involve only gross abnormalities. Because of the limited resolution of metaphase chromosomes, aberrations smaller than 5–10 Mb cannot be detected using conventional CGH.