Conservation of the rat X chromosome gene order in rodent species.

We constructed the comparative cytogenetic maps of X chromosomes in three rodent species, Indian spiny mouse (Mus platythrix), Syrian hamster and Chinese hamster, using 26 mouse cDNA clones. Twenty-six, 22 and 22 out of the 26 genes, which were mapped to human, mouse and rat X chromosomes in our previous study, were newly localized to X chromosomes of Indian spiny mouse, and Syrian and Chinese hamsters, respectively. The order of the genes aligned on the long arm of human X chromosome was highly conserved in rat and the three rodent species except mouse. The present results suggest a possibility that the rat X chromosome retains the ancestral form of the rodent X chromosomes.