Horizontal transfer.

Eukaryotic transposable elements provide some of the best documented examples of the occasional horizontal transfer of DNA sequences between both closely and distantly related species. Although the mechanisms involved in such a transfer remain a puzzle, new ideas are beginning to emerge. The rapidly expanding number of reports of transposable elements that may have been transferred horizontally raises questions both about whether these elements are more prone to this mode of transfer than non-mobile genes, and about the possible evolutionary significance if such a difference is real.