a) They were found to be DNA sequences that code for enzymes which bring about the insertion of an identical copy of themselves into a new DNA site.
b) Transposition events involve both recombination and replication processes which frequently generate two daughter copies of the original transposable elements. One copy remains at the parent site while the other appears at the target site (on the host chromosome).
c) The insertion of transposable elements invariably disrupts the integrity of their target genes. For example, if an IS (= insertion sequence) becomes inserted into an Operon, it interrupts the coding sequence and inactivates the expression of the target gene into which it inserts as well as any gene downstream in that same Operon. This is because an IS contains transcription and/or translation termination signals that block the expression of other genes downstream in an Operon. This “one-way” mutational effect (or polarity) is referred to as a polar mutation.
d) Since transposable elements carry signals for the initiation of RNA synthesis, they sometimes activate previously dormant genes.
e) A transposable element is not a replicon (a sequence that contains a site for the origin of replication), thus, it cannot replicate apart from the host chromosome the way that plasmids and phage can.
f) No homology exists between the transposon and the target site for its insertion. Many transposons can insert at virtually any position in the host chromosome or into a plasmid. Some transposons seem to be more likely to insert at certain positions (hot spots), but rarely at base- specific target sites.