Figure 5 from: Nilsson R, Tedersoo L, Abarenkov K, Ryberg M, Kristiansson E, Hartmann M, Schoch C, Nylander J, Bergsten J, Porter T, Jumpponen A, Vaishampayan P, Ovaskainen O, Hallenberg N, Bengtsson-Palme J, Eriksson K, Larsson K, Larsson E, Kõljalg U (2012) Five simple guidelines for establishing basic authenticity and reliability of newly generated fungal ITS sequences. MycoKeys 4: 37-63. https://doi.org/10.3897/mycokeys.4.3606

Figure 5 - a Graphical overview of the BLAST results of a regular sequence b BLAST results of a chimeric sequence where the ITS1 comes from another species, such that the ITS1 is not involved in the alignment featuring the 5.8S+ITS2 (hence the lack of a match for the first ca. 180 bp.). Obviously, a severely compromised sequence that is already in INSD will always find a perfect match through BLAST in INSD: itself. In that case, the presence of a 100% similar reference sequence cannot be used as a testimony to the authenticity of the query sequence.