Gbanding

G-banding, commonly referred to as GTG-banding, is a chromosome-staining technique used in cytogenetics to generate a reproducible pattern of dark and light stripes along individual chromosomes. The method employs partial proteolytic digestion with trypsin followed by staining with Giemsa dye, producing bands that are consistent across cells of a species. Because each chromosome exhibits a characteristic GTG-band pattern, this technique supports identifying chromosomes and detecting structural abnormalities. G-banding has been a standard tool since the late 20th century and remains widely used in clinical and research settings.

Procedure and interpretation: Cells are cultured and arrested in metaphase, then swollen briefly in a hypotonic solution and fixed. The slides are treated with trypsin to digest a portion of chromosomal proteins and are subsequently stained with Giemsa. The resulting dark bands tend to be AT-rich and gene-poor, while light bands are GC-rich and gene-rich. The pattern provides a unique karyotype for each chromosome, enabling identification of translocations, deletions, duplications, inversions, and other rearrangements. Band coordinates are described using a standard nomenclature that refers to specific chromosomal regions and bands.

Applications and context: GTG-banding is used for routine karyotyping in prenatal diagnostics, oncology, and constitutional cytogenetics. It aids in characterization of chromosomal abnormalities, supports prognostic assessment, and guides further testing with molecular methods. The technique is often combined with higher-resolution approaches to delineate small alterations and with fluorescence in situ hybridization for targeted investigations.

Limitations and evolution: GTG-banding requires dividing cells and subjective interpretation, and its resolution is limited to large to moderate-sized alterations. Advances in molecular cytogenetics, including array comparative genomic hybridization and sequencing-based methods, supplement GTG-banding and increasingly complement or replace it for some diagnostic purposes, though GTG-banding remains a foundational technique in many laboratories.