QBanding

Qbanding, also written as Q-banding, is a chromosome banding technique used in cytogenetics to produce a distinctive pattern of alternating light and dark bands on metaphase chromosomes. The method relies on quinacrine mustard, a fluorescent dye that binds preferentially to AT-rich regions of DNA. When stained chromosomes are viewed under ultraviolet illumination, the AT-rich regions fluoresce as bright bands (the Q bands) while GC-rich regions appear relatively dim. As a result, the Q-band pattern highlights chromosomal structure and is approximately the complement of the patterns produced by G-banding.

In practice, cells are cultured and arrested in metaphase, and chromosomes are spread on slides. The slides are treated with quinacrine and examined with a fluorescence microscope, typically equipped with UV excitation. Photomicrographs are captured to establish a karyotype. The technique is sensitive to staining conditions and fluorescence stability, which can affect band sharpness and reproducibility.

Qbanding was one of the earliest fluorescence-based chromosome banding methods and played an important role in the development of karyotyping. It is complementary to other banding techniques; because Q bands correspond to AT-rich regions, the pattern is roughly inverse to many light/dark patterns seen with G-banding. In modern practice, Q-banding has largely been supplanted by more reproducible and higher-resolution methods such as G-banding and fluorescence in situ hybridization (FISH), though it remains of historical interest and may still be used in some teaching laboratories or specialized applications.

See also: G-banding, R-banding, C-banding, NOR-banding.