Amplification of repetitive DNA and origin of a rare chromosomal sex bivalent in Deltochilum (Calhyboma) verruciferum (Coleoptera, Scarabaeidae).

The most intriguing karyotypic variation in the Coleoptera involves variation in sex chromosome structure, origin and behavior. In this report we describe chromosomal characteristics of Deltochilum (Calhyboma) verruciferum (Coleoptera, Scarabaeidae) using conventional and differential cytogenetic techniques, with emphasis on the description of a rare sex bivalent in the Coleoptera and dispersion of repetitive DNA. This species shows 2n = 20,XY(p) with biarmed chromosomes. Analysis of constitutive heterochromatin through C-banding revealed mainly diphasic autosomes with short heterochromatic arms, while the X was completely heterochromatic and the Y was heterochromatic in the long arm. This pattern was confirmed through the use of CMA(3) fluorochrome that stained all heterochromatic regions. Silver nitrate staining marked all heterochromatic regions and the lumen of the sex bivalent in metaphase I. These results indicated that karyotypic differentiation in D. (C.) verruciferum involved autosomal amplification and dispersion of repetitive DNA and the origin of unusual sex chromosomes (XY(p)), generating a unique karyotype in this species.