Which nucleotides are considered “specifically defined” according to WIPO Standard ST.26?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

According to MPEP 2412.03(a), WIPO Standard ST.26 defines “specifically defined” nucleotides as any nucleotide other than those represented by the symbol “n”. The MPEP provides a table of nucleotide symbols, where:

• Symbols a, c, g, and t/u represent specifically defined nucleotides
• Symbols like m, r, w, s, y, k, v, h, d, and b represent combinations of specifically defined nucleotides
• The symbol n represents “unknown” or “other” and is not considered specifically defined

This definition is crucial for patent applications filed on or after July 1, 2022, containing nucleotide sequence disclosures.