retroposition
Kaessmann H, Vinckenbosch N & Long M 2009 RNA-based gene duplication: mechanistic and evolutionary insights. Nat Rev Genet 10:19-31.
- intron gains are rare events during evolution
- intron loss seems to be more frequent
- in mammals, for example, not a single case of intron gain has been documented, whereas more than 100 intron losses have been reported