THE LINKAGE MAP OF SHEEP CHROMOSOME-6 COMPARED WITH ORTHOLOGOUS REGIONS IN OTHER SPECIES

The genetic linkage map of sheep Chromosome (Chr) 6 has been extended to include 35 loci with the addition of 11 RFLP and 12 microsatellite loci. The sex-averaged linkage map now spans 154 cM from phosphodieste rase cyclic GMP beta polypeptide (PDE6B) to OarCP125, an anonymous she ep microsatellite. The male and female map lengths, at 180 cM and 132 cM respectively, did not differ significantly. The physical assignment of PDE6B to Chr 6q33-qter orientates the linkage map on sheep Chr 6 w ith PDE6B near the telomere and OarCP125 towards the centromere. The o rder and genetic distances between loci are similar for the sheep Chr 6 and cattle Chr 6 maps, except for the position of the casein genes. The sheep Chr 6 linkage map is also comparable to portions of human Ch r 4, mouse Chrs 5 and 3, and pig Chr 8. The synteny between sheep Chr 6 and human Chr 4 has been extended from PDE6B (4P16.3) to epidermal g rowth factor (EGF, 4q25-q27). However, a region from platelet-derived growth factor receptor alpha polypeptide (PDGFRA) to bone morphogeneti c protein 3 (BMP3), which spans 19 cM on sheep Chr 6, appears to be in verted with respect to the human and mouse loci. Other differences in the gene order between sheep, pig, and mouse suggest more complex rear rangements.