A sample of 28 yaks (Bos grunniens) (9 males and 19
females), kept in the province of Teramo (Italy), was
cytogenetically analyzed in order to investigate similarities
or differences with cattle (Bos taurus). The
results were as follows: (a) the chromosomal makeup
of the yak was 2n060,XY, as for cattle; (b) no
numerical as well as structural chromosomal abnormalities
were found in the sample investigated; (c) the
incidence of chromosome + chromatid breaks was 3.7
vs 3.0 % as for cattle; (d) the GTG- RBG- and RBAbanded
karyotypes were all similar to the cattle standard
karyotypes; (e) the CBA-banding pattern was
similar to that of cattle; (f) the mean rate of SCE/cell
at 10 μg/ml (f.c.) of BrdU was 5.2±2,23 (range 1–13),
similar to that of cattle; (g) silver staining revealed the
presence of telomeric NORs on five pairs of autosomes
n. 2,3,4,11 and 25, as for cattle; (h) Zoo-FISH
with bovine painting probes derived from microdissected chromosomes 5-X-Xcen and Y- upon
yak metaphase chromosomes showed complete hybridization;
(i) FISH-mapping of bovine BAC-clones
containing ZFY- and SRY- genes revealed the same
location on the yak Y-chromosome. All these data
demonstrate the close evolutionary relationships between
yak and cattle. However, the fact that Bos
taurus x Bos grunniens F1 male hybrids are sterile,
while the females are normally fertile, would suggest
that the genomes of the two species are not completely
homologous and that minute structural differences
might exist in the chromosomes of the two species
which are worth to be further investigated