Chromosomal variability of sex chromosomes and NOR's in Trichomys apereoides (Rodentia, Echimyidae).

G-banding, C-banding, and silver staining techniques were used to analyze the chromosomes of Trichomys apereoides. In a sample of 22 specimens the diploid number was 2n = 30, with several pairs of biarmed chromosomes and a large metacentric (pair 1) with a secondary constriction, or nucleolar organizing region (NOR), in the short arm. One male had a heteromorphic pair 1, with only one NOR-bearing homolog. C-bands showed constitutive heterochromatin in the centromeric region of almost all autosomes. The X has a large block in the proximal region and an interstitial small band in the long arm. The Y is totally heterochromatic. One heteromorphic female with an increased C-band block in one of the X chromosomes was observed. The Y is a small submetacentric; one male showed a metacentric Y, resulting probably from a pericentric inversion. The sexual bivalent and the synaptonemal complexes of all autosomal bivalents were revealed by silver staining in pachytene cells.