RESOLVING AMBIGUITIES IN THE KARYOTYPE OF DOMESTIC SHEEP (OVIS-ARIES)

The unambiguous identification of ovine chromosomes has become essenti al for the mapping of the sheep genome, which predominantly consists o f telocentric chromosomes of gradually decreasing size. Nucleolus orga nizer regions (NORs) and Robertsonian fusions have been used here as t he cytological and morphological markers, respectively, to define the banding pattern of eight paris of sheep telocentric chromosomes that h ave an ambiguous identification status. Five Robertsonian chromosomes involving most of the ambiguous chromosomes as well as normal prometap hase chromosomes were stained sequentially and separately by QFQ, GTG, and Ag-NOR methodologies. The prometaphase banding patterns of the am biguous chromosomes 4, 6, 8, 9, 21, 24, 25 and 26 are represented sche matically. For providing an accurate image of the banding pattern, a s ystem of shading has been employed to show the relative intensity of b ands in a given chromosome. The results presented here will facilitate the regional mapping of the sheep genome, extend the information on c ytogenetic homology with other bovids, and substantially accelerate th e comparative mapping studies in Bovidae.