text: An unnatural base pair (UBP) is a designed subunit (or nucleobase) of DNA which is created in a laboratory and does not occur in nature. Examples include d5SICS and dNaM. These artificial nucleotides bearing hydrophobic nucleobases, feature two fused aromatic rings that form a (d5SICS–dNaM) complex or base pair in DNA. E. coli have been induced to replicate a plasmid containing UBPs through multiple generations. This is the first known example of a living organism passing along an expanded genetic code to subsequent generations.