Deer mice (Peromyscus maniculatus) and congeneric species are the most common North American mammals. They represent an emerging system for the genetic analyses of the physiological and behavioral bases of habitat adaptation. Phylogenetic evidence suggests a much more ancient divergence of Peromyscus from laboratory mice (Mus) and rats (Rattus) than that separating latter two. Nevertheless, early karyotypic analyses of the three groups suggest Peromyscus to be exhibit greater similarities with Rattus than with Mus.Comparative linkage mapping of an estimated 35% of the deer mouse genome was done with respect to the Rattus and Mus genomes. We particularly focused on regions that span synteny breakpoint regions between the rat and mouse genomes. The linkage analysis revealed the Peromyscus genome to have a higher degree of synteny and gene order conservation with the Rattus genome.These data suggest that: 1. the Rattus and Peromyscus genomes more closely represent ancestral Muroid and rodent genomes than that of Mus. 2. the high level of genome rearrangement observed in Muroid rodents is especially pronounced in Mus. 3. evolution of genome organization can operate independently of more commonly assayed measures of genetic change (e.g. SNP frequency).