Modern Medical Laboratory Journal

A genetic screen can potentially diagnose more than 1,200 genetic disorders and chromosomal abnormalities. Karyotyping uses g-band analysis of metaphase chromosomal spreads, usually in 20 cells to identify chromosomal abnormalities such as trisomies, monosomies, translocations, and very large deletions and duplications. 

Karyotyping involves analysis of the entire chromosome complement through the microscope. Dividing cells are harvested during metaphase, the time of greatest chromosome condensation, by disruption of the spindle using drugs such as colchicine. Chromosomes are visualized by staining, including the use of special stains to elicit banding patterns. In general GC-rich regions tend to be gene rich and stain darkly with G-banding, bright with R-banding, and dark with Q-banding.

Karyotyping is able to detect polyploidy, aneuploidy, translocations, inversions, rings, and copy number changes in the size range of 4–6 Mb; smaller copy number changes require the use of molecular cytogenetic techniques.
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