There is provided a transposable element comprising at least four inverted repeats, at least two of which are each inverted in relation to another, the element comprising DNA for insertion into a host genome, the DNA being located between two pairs of opposing repeats excisable by a transposase in situ to leave said DNA without flanking transposon-derived repeats in the host genome. Also provided is a transposable element comprising at least three inverted repeats, at least one of which is inverted in relation to the others, wherein at least one non-terminal repeat is a minimal repeat. Both these elements allow for greater efficiency of insertion of nucleotide sequences into the genome.