GENE-BASED ANCHORING OF THE RAT GENETIC-LINKAGE AND CYTOGENETIC MANS - NEW REGIONAL LOCALIZATIONS, ORIENTATION OF THE LINKAGE GROUPS, AND INSIGHTS INTO MAMMALIAN CHROMOSOME EVOLUTION

In order to generate anchor points connecting the rat cytogenetic and genetic maps, the cytogenetic position of 62 rat markers (including 55 genes) already localized genetically was determined by fluorescence i n situ hybridization. Whenever possible, markers located near one end of the linkage groups were included. These new localizations allowed u s to unambiguously orient the 20 autosomal and the X chromosome linkag e groups. The position of the centromere in the linkage map could also be determined in the case of several metacentric chromosomes. In addi tion, the regional localization of 15 other rat genes was determined. These new data bring useful information with respect to comparative ma pping with the mouse and the human and to mammalian evolution. They il lustrate, for instance, that groups of genes can remain syntenic durin g mammalian evolution while being subjected to intrachromosomal rearra ngements in some lineages (synteny is conserved while gene order is no t:). This analysis also disclosed cases of synteny conservation in one the two rodent species and the human, while the synteny is split in t he other rodent species: such configurations are likely examples of li neage-specific interchromosomal rearrangements associated with speciat ion.