Linkage relations between A2M, HOX3, INT1, KRAS2, and PAH on bovine chromosome 5

There is a high level of conservation between human chromosomes and bovine syntenic groups. One such comparison is between human chromosome 12 and bovine chromosome 5, where at least 16 loci have been shown to be conserved in an homologous segment. However, the degree of conservation of order of the loci on bovine chromosome 5 is unknown, and in general the conservation of order in comparisons between humans and cattle can only be speculated. We have estimated the recombination fractions between five of the loci that were previously published as mapping to bovine chromosome 5 by a combination of in situ hybridization and analysis of bovine-rodent somatic cell hybrid lines to determine whether order has been conserved in the homologous segment of bovine chromosome 5 and human chromosome 12. Recombination fractions were estimated in reference pedigrees of cattle. The loci were A2M, GSNL, HOX3, INT1, KRAS2, and PAH. Restriction fragment length polymorphisms for all loci were defined by screening a panel of eight restriction endonucleases. The linkage between loci was estimated using the lod score method, and all possible pairwise comparisons were made. A preliminary map was created by joining together loci that showed the smallest recombination fractions and the largest lod scores. A multipoint analysis was performed to estimate support for the most likely order. This order shows the relative inversion of some of the loci. Moreover, the distance spanned in cattle is less than a quarter the distance spanned in humans. Together, these data indicate that several chromosomal evolutionary events have occurred in the homologous segment shared by humans and cattle.