Oligonucleotide constructs are described, each comprising a functional element and a coding element, wherein the functional element comprises a functional sequence, the functional sequence comprising a sequence of nucleotides in which one or more, or each, nucleotide is modified and the coding element comprises a coding sequence, the coding sequence comprising a sequence of nucleotides which do not contain the modifications of the functional sequence, wherein the coding sequence encodes the sequence structure of the functional sequence.