Chromosomal evolution in duiker antelope (Cephalophinae: Bovidae): karyotype comparisons, fluorescence in situ hybridization, and rampant X chromosome variation.

Fluorescence in situ hybridization (FISH) and conventional banding techniques were used to identify patterns of similarity among the genomes of six species of antelope, subfamily Cephalophinae. The G-banded euchromatic portions of the autosomes were invariable in all species; however, significant modifications of the X chromosomes were detected. Two of the taxa, Cephalophus maxwellii and C. monticola, were characterized by acrocentric X's, while X chromosome morphology varied from submetacentric to metacentric in the remaining species (C. dorsalis, C. natalensis, Sylvicapra grimmia, and C. silvicultor). The short arm of the X was heterochromatic in each species. Total genomic DNAs from these antelope were used as hybridization probes against Cephalophus metaphase chromosomes and resulted in robust fluorescence in the pericentromeric region of each autosome and in the heterochromatic short arm of the X chromosome, indicating complimentarity of DNA sequences in these regions. Conversely, chromosome painting involving genomic DNAs derived from the subfamilies Alcelaphinae (Pygargus dorcas) and Neotraginae (Oreotragus oreotragus) showed a marked absence of hybridization at these sites. Additionally, X chromosome comparisons between the Cephalophinae and Bovinae (represented by Bos taurus) revealed two euchromatic pericentric inversions which had occurred since their common ancestry. There is good G-band homoeology between the inverted cattle chromosome region Xq12 --> q34 and most of the proximal portion of Xq in duikers, as well as between the distal third of the duiker Xq and the cattle Xp. The latter rearrangement was further confirmed by in situ hybridization using a probe containing an insert spanning bands p12 to p14 of the cattle X chromosome.