Mys, a jumping gene referred to as a retrotransposon, was initially identified in the deer mouse genus Peromyscus. Previous studies via Southern blot analysis suggested that mys is found in related genera. In this study, mys was analyzed in species of Peromyscus using an intra-mys PCR strategy. We clearly demonstrate mys is found not only in representatives of the Peromuscus subgenus of the Peromyscus genus, but this is also the first study to identify the element within members of the subgenus Haplomylomys. Preliminary findings seem to provide evidence that mys originated in rodents that predate the ancestor of the Peromyscus species; mys subfamilies derived from different source genes were identified in Peromyscus maniculatus, and their origins will be evaluated in future testing. The application of retrotransposons in gene therapy and for phylogenetic analysis are numerous, therefore scrutiny of their form and function is necessary for a more in-depth understanding of these potential tools. The purpose of this study is to gain further insights regarding evolution of retrotransposons via the mys element.