Cytogenetic Variation in Blue Sheep (Pseudois nayaur szechuanensis): Implications for Karyotype Evolution, Taxonomy and Captive Breeding

Background: The analysis of chromosomal variation can help to assess genetic diversity, understand evolutionary processes and phylogenetic relationships, and manage the conservation of animal populations. In the genus Pseudois, karyotypic characteristics and evolutionary relationships still remain insufficiently understood. Methods: In this study, the karyotypes of ten captive blue sheep (Pseudois nayaur szechuanensis) were examined using GTG- and C-banding, NOR staining, and cross-species fluorescence in situ hybridisation (FISH) with bovine chromosome painting and BAC probes. Results: In six animals, the diploid chromosome number was 2n = 54 with three biarmed autosomal pairs resulting from Robertsonian (centric) fusions involving chromosomes orthologous to BTA1;26, BTA2;28, and BTA5;14. Four individuals (two males and two females) exhibited 2n = 55 and were heterozygous for the BTA5;14 Robertsonian rearrangement. Based on the published literature and the results of the present study, three distinct karyotypes with diploid chromosome numbers of 2n = 54, 2n = 55 and 2n = 56 have been documented in blue sheep. Conclusions: The observed differences in chromosome number demonstrate karyotypic variation in this species and highlight the value of karyotype analysis in captive animals for monitoring the distribution of chromosomal variants and preserving the chromosomal constitution of captive-bred populations.