Centric fusion differences among Oryx dammah, O-gazella, and O-leucoryx (Artiodactyla, Bovidae)

G- and C-banded karyotypes of the genus Oryx were compared using the standa rd karyotype of Bos taurus. Chromosomal complements were 2n = 56 in O. gaze lla gazella, 2n = 58 in O. g. beisa and O. g. callotis, 2n = 56-58 in O. da mmah, and 2n = 57-58 in O. leucoryx. The number of autosomal arms in all ka ryotypes was 58. Nearly all variation in diploid number was the result of t hree independent centric fusions, but one 2n = 57 specimen of O. g. gazella deviated from the normal complement of 2n = 56 due to XXY aneuploidy. A 2; 17 centric fusion was fixed in O. g. gazella, whereas O. g, beisa and O. g. callotis lacked this fusion and had indistinguishable karyotypes. Oryx dam mah was polymorphic for a 2;15 centric fusion, and O. leucoryx was polymorp hic for an 18;19 centric fusion. The five Oryx taxa shared a fixed 1;25 cen tric fusion; the small acrocentric element involved in the 1;25 fusion was identified by fluorescence in situ hybridization using a cosmid specific to Bos chromosome 25. The X and Y chromosomes were also conserved among the f ive taxa. Oryx g. gazella differed from the other Oryx species because of t he fixed 2;17 centric fusion. This difference reflects an apparently longer period of geographic isolation between O. g. gazella and other populations of Oryx, and it is consistent with the classification of O. gazella and O. beisa as distinct species (see Kingdon, 1997). The lack of monobrachial re lationships among the Oryx taxa indicates that sterility barriers between s pecies have not developed. Viability of hybrid offspring constitutes a thre at to captive breeding programs designed for endangered species. conservati on; in the case of Oryx, the 2;15, 2;17, and 18;19 metacentrics could serve as marker chromosomes for assessing hybridization between certain Oryx tax a.