A karyotypic analysis of nilgai, Boselaphus tragocamelus (Artiodactyla : Bovidae)

A combination of chromosomal banding and fluorescence in situ hybridization (FISH) was used to characterize the karyotype of Boselaphus tragocamelus ( nilgai) relative to the domestic cattle standard karyotype. G-, Q- and C-ba nd karyotypes of nilgai are presented, and the chromosomal complement of ni lgai is determined to be 2n = 46 (female FN = 60, male FN = 59; NAA = 56), consistent with previous reports for the species. Comparisons with cattle i dentified extensive monobrachial homologies with some noteworthy exceptions . Chromosome 25 is centrically fused to 24, and chromosome 16 is acrocentri c. Both appear to have additional pericentromeric material not seen in the equivalent cattle acrocentrics. This pericentromeric chromatin may be the r esult of de novo additions or translocation of pericentromeric material fro m chromosome 6, which is shown to be centrically fused to 13 but is only ab out two-thirds the length of cattle 6. Comparisons with cattle demonstrated that nilgai chromosome 17 has undergone a paracentric inversion and that c hromosome 20 has two blocks of interstitial constitutive heterochromatin. T he identities of both chromosomes were confirmed by chromosomal FISH. Furth ermore, chromosomal banding and FISH were used to determine that autosome 1 4 has been fused to the ancestral X and Y of nilgai to form compound neo-X and -Y chromosomes. Additional FISH analyses were conducted to confirm othe r proposed chromosome homologies and to identify nucleolar organizing regio ns within the nilgai complement.