bandning

Banding is a set of cytogenetic techniques that produce a reproducible pattern of light and dark bands along the length of chromosomes. The resulting banding patterns allow each chromosome to be identified by a characteristic sequence of bands and enable detection of structural alterations such as deletions, duplications, inversions, and translocations. Banding is typically performed on metaphase chromosome preparations or, in some methods, on extended chromatin.

The most widely used banding methods are G-banding, Q-banding, R-banding, and C-banding. G-banding uses Giemsa stain after controlled enzymatic digestion (often with trypsin) to create a stereotyped pattern of dark and light bands. Q-banding relies on the fluorescent staining of DNA with quinacrine. R-banding provides a reverse pattern to G-banding, usually obtained by heat or acid treatment before staining. C-banding highlights constitutive heterochromatin, particularly around centromeres, by selective pretreatment that enriches these regions. Each method yields a reproducible atlas of chromosome bands that is used to assign chromosomal locations and to interpret abnormalities.

Applications include routine karyotyping in clinical genetics to diagnose numerical and structural chromosomal disorders, cancer cytogenetics to identify characteristic translocations, and comparative genomics to study chromosome evolution. Banding also supports chromosomal mapping and the study of chromosomal architecture.

Limitations include the requirement for actively dividing cells to obtain metaphase spreads and a resolution limit on the order of several megabases per band. Submicroscopic rearrangements may be missed, necessitating complementary techniques such as fluorescence in situ hybridization (FISH) or array-based methods for higher resolution analysis. See also karyotype analysis and fluorescence in situ hybridization.