dicentric

Dicentric describes a chromosome or chromosome fragment that bears two centromeres (kinetochores). In most organisms, chromosomes are monocentric, with a single centromere essential for proper segregation. Dicentrics arise when two chromosome fragments fuse or when misrepair of DNA double-strand breaks produces a chromosome carrying two centromeres. They can form after exposure to ionizing radiation, certain chemicals, or during chromosomal rearrangements in meiosis or somatic division, and they are observed in plants, animals, and cancer cells.

During mitosis, both centromeres attach to spindle fibers pulling toward opposite poles. This creates mechanical tension and typically results in an anaphase bridge that breaks, provoking further rearrangements, fragmentation, and often cell death or instability. Some dicentrics are stabilized by inactivating one centromere (centromere inactivation) or by selection for a single active centromere (neocentromere formation), allowing the chromosome to persist albeit abnormally. Dicentrics contribute to genomic instability and are a characteristic feature of radiation-induced damage and some cancers.

Applications include cytogenetic biodosimetry: counting dicentric chromosomes in peripheral blood lymphocytes to estimate radiation dose. Detection methods include karyotyping and fluorescence in situ hybridization (FISH). The term also contrasts with acentric fragments, which lack a centromere, and with monocentric chromosomes.