Fig. 2. The DNA barcode is rationally designed. (A) Diagram of DNA barcode – containing universal primer sites, spacer regions, and an 8 nucleotide barcode sequence. Most of the barcode is made of constant regions, which do not change barcode to barcode (B) we used 8 different barcode sequences. Each barcode region was 8 nucleotides. (C) The 8 nucleotide sequences were designed with a base distance of 3 or more, so all barcodes could be sequenced at once. (D) DNA and 2′-O-methyl ribose nucleotides. (E) Diagram of DNA containing both phosphorothioate and phosphodiester linkages. (F) Diagram of 7 chemical modification patterns used in this study.