Transposon domestication expands the functional reservoir in mammalian genomes

Since the discovery of transposons, their sheer abundance in host genomes has puzzled many. While historically viewed as largely harmless “parasitic” DNAs during evolution, transposons are not a mere record of ancient genome invasion. Instead, nearly every element of transposon biology has been integrated into host biology. Here we review how sequences introduced by transposon activities provide raw material for genome innovation and document the distinct evolutionary path of each species.