Transfer RNA genes in pieces are an ancestral character.

randau & Söll (2008) suggest that the anticodon loop region of transfer rNa (trNa) genes is the target site of a huge variety of mobile genetic elements and that this resulted in the evolution of trNa genes in pieces. they therefore suggest that the presence of introns in the anticodon loop might not be a plesiomorphic trait that is important in trNa origin (Di giulio, 2006), but an acquired trait, as it endowed trNa genes with a precious protection mechanism against the integration of viruses and other autonomous genetic elements, in that the intron removed the integration site of these mobile genetic elements. Similarly, randau & Söll maintain that split and per­ muted trNa genes might also have been able to prevent the integration of mobile genetic elements, as their attachment sites were evidently disrupted and hence restricted their propagation within the genome, thus conferring a selective advan­ tage. this evolution should not have been possible as randau & Söll consider split trNa genes to be derived from trNa genes containing the intron, which, once inserted into the anticodon loop region of trNa genes, would have disrupted the attachment site for mobile genetic elements. after this disruption there would have been no selec­ tive pressure to continue the evolutionary process—that is, to actually fragment the trNa genes. More generally, it is expected that the ease with which introns might have been inserted into trNa genes compared with the complexity of evolving trNa genes in pieces (Di giulio, 2006, 2008) would lead to the conclusion that the insertion of introns would always have been preferred to the evolution of trNa genes in pieces as a mechanism to remove the attachment sites of mobile genetic elements. Furthermore, if the intron in the anti­ codon loop of trNa were truly an acquired trait, as randau & Söll maintain, this would lead to the prediction that an organism such other words, the intron present in the anti­ codon loop of trNa genes might well be a plesiomorphic trait, whereas the same type of intron present in other parts of the molecule might be an apomorphy. this is in perfect agreement with the observation that the introns present in the anticodon loop of trNa genes of archaea and Eukarya are of the same type (Haugen et al, 2005) and are therefore probably extremely ancient.