In this section:
The transposable elements of GEP are fragments of the genome that can be activated and jump to another place in the chromosome. In GEP there are three kinds of transposable elements: (1) short fragments with a function or terminal in the first position that transpose to the head of genes, except the root (insertion sequence elements or IS elements); (2) short fragments with a function in the first position that transpose to the root of genes (root IS elements or RIS elements); and (3) entire genes that transpose to the beginning of chromosomes.
The existence of IS and RIS elements is a remnant of the developmental process of GEP, as the first GEA used only single-gene chromosomes and, in such systems, a gene with a terminal at the root was of little use. Consequently, transposition to the root was tightly controlled and only transposons with a function in the first position were chosen to transpose to the root. When multigenic chromosomes were introduced, this feature was maintained as these operators not only serve different purposes in evolution but are also important to the understanding of the mechanisms of genetic variation. Indeed, the comparison of the transforming power of these operators (see
chapter 7) shows clearly that there is no need to be cautious while designing genetic operators, rejecting everything which seems to give rise to too drastic modifications. In fact, root insertion – the most disruptive operator in GEP – is capable of finding solutions very efficiently. Moreover, IS and RIS transposition are also capable of creating simple repetitive sequences in the genome and this, in itself, is not only curious but also important to evolution.