The enigma of the B chromosome-specific behaviour

Supernumerary (B) chromosomes are widespread genomic elements that persist through non-Mendelian inheritance by exploiting host cellular mechanisms, yet the basis of their selective transmission and elimination remains poorly understood. This review integrates current knowledge on chromosome-specific behaviour, with particular emphasis on the centromere function, kinetochore assembly, epigenetic chromatin states, non-coding RNAs, and sequence composition. We examine how perturbations in these systems can skew chromosome segregation, or lead to chromosome elimination, and consider growing evidence that B chromosomes may themselves encode or modulate factors influencing these processes. Their repeat-rich architecture and enrichment in chromosome-specific satellite DNA are also discussed as contributors to their recognition by the cellular machinery. By unifying structural, epigenetic, and genetic perspectives, this review outlines a framework for understanding chromosome drive and elimination and highlights key directions for future research.