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Supernumerary B chromosomes are dispensable elements of the genome which can be retained in populations at high frequencies, despite being deleterious, through the ability to undergo non-Mendelian inheritance. Their mode of origin is, however, obscure. Recent work on gynogenetic fish has demonstrated the incorporation of small, unstable, centromere-containing microchromosomes, probably of interspecific derivation, into an asexual lineage (1). That these resemble B chromosomes both in structure and behaviour is consistent with the proposal that hybridisation between closely related species may be a significant mode of origin for such selfish genetic elements. Additional work on the B chromosome of a parasitoid wasp and observations on patterns of chromosome breakage from somatic cell hybrids also support this hypothesis.

Original publication




Journal article


BioEssays : news and reviews in molecular, cellular and developmental biology

Publication Date





579 - 582


Dept of Genetics, University of Cambridge, UK.


Chromosomes, Animals, Fishes, Gene Frequency, Sex Determination Analysis