A cytogenetic investigation on the yak (Bos grunniens) reared in central Italy

The domestic yak (Bos grunniens) is an importantBovidae species which in Asia plays a remarkable rolefor the economy of the Tibetan highlands (over 4000 mabove sea level.). Despite its strategic and economicalimportance, this species has been almost neglected, froma cytogenetic point of view, as demonstrated by the fewpapers present in the literature. To fill this gap, weundertook a cytogenetic investigation by using bloodsamples of eight yak bulls recently imported into centralItaly. CGR-banding, silver staining and FISH-techniqueswere applied. The preliminary results were as follows: (a)the chromosomal make-up of the yak was 2n=60,XY,(b) the animals investigated showed normal karyotype,(c) the frequency of chromosome/chromatid breaks wassimilar to that of cattle (3.7 vs 3.0 %, respectively), (d)the mean rate of SCE/cell at 10 2g/ml (f.c.) wassignificantly (Pe0.001) lower compared to that of cattle(5.2 vs 8.3, respectively), (e) the GTG-RBA-RBG bandingpatterns Y at the 400 bands level of resolution Y didnot reveal structural differences compared to cattle, (f)the CBA-banding pattern was also similar to cattle, i.e.no C-bands on the subcentromeric X, while the Y- chromosomeshowed heterochromatic tips in the short arms.Zoo-FISH with bovine painting probes derived frommicrodissected chromosomes 5-X-Xcen and Y- uponyak metaphase chromosomes showed complete hybridization,thus confirming the close homology between thetwo species. In addition, FISH-mapping with bovineBAC-clones containing ZFY and SRY genes to the yakY-chromosome also revealed the same localization asreported in cattle (Yp12.2 and Yq23dist, respectively).However, the fact that Bos taurus x Bos grunniens F1 malehybrids are sterile, while the females are normally fertile,suggests that the main difference between yak and cattlemight be in the X-Y pseudoautosomal (PAR) region ofthe two species. Further investigation, therefore, is necessarywith more effective cytogenetic techniques, such ashigh resolution banding, fine gene mapping analysis andDNA sequencing.