Chromosome polymorphism in Holochilus venezuelae (Rodentia: Cricetidae): C- and G-bands

Karyological analysis of C- and G-banding patterns of 44 specimens of Holochilus venezuelae revealed six distinct karyomorphs, which were designated as follows: I (2n = 44; fundamental number (FN) = 56); II (2n = 45; FN = 58); IV (2n = 43; FN = 56);V(2n = 44; FN = 58); IV-a(2n = 42; FN = 56); and V-a (2n = 44; FN = 58). This chromosomal polymorphism is interpreted as the result of (i) one or two Robertsonian changes of the centric-fusion type, originating from one member of chromosome pair 10 and one of pair 11 (in karyotypes IV and V) and two metacentric chromosomes from pairs 10 and 11 (in karyotype IV-a); (ii) one pericentric inversion (in karyotype V-a) forming one submetacentric chromosome from the metacentric fusion product described above; and (iii) the presence of B chromosomes, which are almost completely heterochromatic and do not pair with any member of group A. The pattern of C-banding reveals that the first five pairs of metacentric chromosomes contain very little centromeric heterochromatin, while pair 6 and the fusion chromosomes (10/11 F) present a thick band. Extensive homology was found between G-banding patterns of Holochilus brasiliensis from Brazil and H. venezuelae. These facts support the hypothesis of a karyotypic evolution via centric fusions previously proposed for this genus.Key words: accessory chromosome, C- and G-banding, polymorphism, Holochilus venezuelae.