cytogenetics

Cytogenetics is a branch of genetics that studies the structure and function of chromosomes, including their number, shape, and behavior during cell division, and how chromosomal abnormalities contribute to disease and development. The field integrates cytology and molecular biology to examine how genome organization influences heredity and pathology.

Historically, cytogenetics emerged with early observations of chromosomes and polygenic traits, with major milestones such as the description of trisomy 21 in Down syndrome and the determination of the human chromosome number (46) in the 1950s. The development of banding techniques in the 1970s, especially G-banding, allowed routine identification of individual chromosomes and structural rearrangements.

Techniques include karyotyping from metaphase spreads after cell culture, banding methods (G-, R-, and Q-banding), and more recently fluorescence-based approaches such as fluorescence in situ hybridization (FISH) and multicolor FISH (including spectral karyotyping).

Molecular cytogenetics extends these methods with comparative genomic hybridization (CGH) and array-CGH to detect copy-number changes, as well as targeted and whole-genome sequencing in some contexts. Single-cell and live-cell cytogenetic methods are enabling studies of mosaicism and dynamic chromosome behavior.

Applications span clinical diagnosis and management: constitutional chromosomal abnormalities giving rise to developmental disorders, reproductive medicine and prenatal testing, cancer cytogenetics where characteristic chromosomal alterations guide prognosis and therapy, and research into genome organization, evolution, and gene mapping. Limitations include resolution constraints and the need for specialized infrastructure and expertise. Cytogenetics remains complementary to molecular genetics, providing a direct view of chromosome structure and its perturbations.