3q21

3q21 is a cytogenetic band on the long arm of human chromosome 3. In human karyotypes, chromosomes are divided into a hierarchical set of bands; 3q21 designates the region on the long (q) arm between the 3q21.1 and 3q21.3 bands, with exact coordinates varying by reference genome and nomenclature. The region is defined by chromosomal staining patterns and by molecular mapping techniques used in cytogenetics.

Genes and function: The 3q21 region contains multiple genes that contribute to a variety of cellular processes. The specific gene content varies with genome build, and researchers map disease-associated variants to this region to understand potential phenotypic effects. Because it lies within a large chromosome, 3q21 is routinely examined when evaluating chromosomal abnormalities in clinical testing and research.

Clinical significance: Structural rearrangements that involve 3q21, including deletions, duplications, and translocations, have been reported in scientific literature. Such alterations can be associated with developmental or congenital features, and may play a role in cancer biology depending on the genes affected. The region is therefore of interest in diagnostic workflows and in studies of genome structure and disease.

Diagnostics and research: Modern genomic techniques—such as fluorescence in situ hybridization (FISH), array comparative genomic hybridization (array-CGH), and sequencing-based methods—are used to detect copy-number changes or breakpoints within 3q21. These tools help characterize chromosomal abnormalities that involve this region and facilitate genotype–phenotype correlations.

See also: Chromosome 3, Cytogenetic bands.