The Di Giulio's model of tRNA origin by dimerization of hairpins. A: The model [51, 52]. The anticodon is supposed to be located on the 3' strand of the hairpin just before the terminal 5'DCCA3' motif. B: The scheme showing that the Di Giulio model necessarily suggests internal duplications in original hairpins. The anticodons are shown red, their complements - green.