A recent duplication of Adam9 through retroposition.

Locations of Adams 9a and 9b in the opossum genome, as well as the gene structure of Adam9b, are shown. Structure of the Adam9a mRNA is also shown for comparison, with black vertical lines representing splice sites (not to scale). The Adam9b pseudogene contains a polyA sequence, and the only intron was identified as an opossum retroposon (Mdo3LTR1a/ERV1), which was likely inserted after the original retroposition event that generated Adam9b. This insertion caused a frameshift.