Retroelements are a major source of genetic variability in eukaryotes. It is a particular class of repeat mobile DNA that is amplified via reverse transcription of an intermediary RNA; it combines various types of elements, from small retroposons of the SINE type (short interspersed nuclear elements) to long retroposons with LTR (long terminal repeat). They are generally present in a large number of copies (several hundreds or even thousands) and represent more than 70% of the genome in some species. Because of their replicative mode of transposition, retroelements create
irreversible insertions, making it possible to trace genetic relationships. On the other hand, their insertion polymorphisms, which reflect events of transposition that have taken place after the divergence between two genotypes, can be used to evaluate divergences between these genotypes.