ZCCHC5 is a member of a family of gag-related retrotransposon genes. These genes appear to have lost the ability to retrotranspose; however, their open reading frames have remained intact, which may indicate that these genes have acquired new functions in the cell. A family of at least eleven genes called Mar related to long terminal repeat retrotransposons from the Ty3/gypsy group, including two genes previously identified as such, is present in human and mouse genomes. Single orthologous copies were identified for most Mar genes in different mammals. All of them have lost essential structural features necessary for autonomous retrotransposition before divergence between mouse and human. Three Mar genes also have introns at identical positions in human and mouse.