COMPARATIVE FISH MAPPING OF MOUSE AND RAT HOMOLOGS OF 25 HUMAN X-LINKED GENES

We constructed a comparative cytogenetic map of 25 functional genes in mouse and rat X chromosomes by direct R-banding fluorescence in situ hybridization. Nineteen and 22 out of the 25 genes, which have been ma pped on the human X chromosome, were newly localized to mouse and rat X chromosomes, respectively. Twenty-two additional genes were integrat ed in the rat-mouse-human comparative map of the X chromosome in this study. Comparison of the gene order indicated the presence of four chr omosome segments with conserved linkage homology between mouse and rat X chromosomes, suggesting that a minimum of four chromosomal inversio n events occurred between mouse and rat X chromosomes during the evolu tion of the two species. Four chromosome segments with conserved linka ge homology were found between human and rat X chromosomes.