Two kinds of polymorphisms have been found in a wild population of Allium subvillosum L. (Liliaceae): (i) extra C-bands and supernumerary chromosome segments on three chromosome pairs and (ii) the absence of the nucleolar organizing region (NOR) in one member of the third chromosome pair (there are two other NOR-bearing chromosome pairs in the karyotype of this species). The fluorescence pattern (chromomycin A3 (CMA3) positive and 4,6-diamidino-2-phenylindole (DAPI) negative) of the extra heterochromatin is similar to that of the standard. The absence of the NOR on the third chromosome pair is related to a variation in the NOR-associated heterochromatin (the chromosomes with no NOR do not have the distal C-band from the satellite, but the proximal C-band may be present). The characteristics of the karyotype of this species, its heterochromatin distribution, and the possible mechanisms by which the polymorphisms may originate are discussed.Key words: Allium, supernumerary segments, heterochromatin, polymorphisms, nucleolar organizing regions.
Identification of Highly Variable Supernumerary Chromosome Segments in an Asexual Pathogen
