CHROMOSOME-BANDING AND GENE LOCALIZATIONS SUPPORT EXTENSIVE CONSERVATION OF CHROMOSOME STRUCTURE BETWEEN CATTLE AND SHEEP

By using three gene probes, one derived from the porcine major histocompatibility complex (MHC) and two from bovine cytokeratin genes, type I (KRTA) and type II (KRTB), the hypothesis of conservation of genome structure in two members of the family Bovidae was examined. Gene mapping data revealed the MHC to be in chromosome region 23q15 --> q23 in cattle (BOLA) and 20q15 --> q23 in sheep (OLA). KRTA was localized to chromosome region 19q25 --> q29 in cattle and 11q25 --> q29 in sheep and KRTB to 5q14 --> q22 in cattle and 3q14 --> q22 in sheep. The banding patterns of the chromosome arms to which the loci were assigned were identical in both species. Moreover, the resemblances of GTG- or QFQ-banding patterns between the cattle and sheep karyotypes illustrated further chromosome homologies. These studies, based on gene mapping comparisons and comparative cytogenetics, document that within bovid chromosomes, homology of banding patterns corresponds to a homologous genetic structure. Hence, we propose that gene assignments on identified chromosomal segments in one species of the Bovidae can be extrapolated, in general, to other bovid species based on the banding homologies presented here.