How should ambiguity symbols be used in nucleotide sequences?

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.

The MPEP 2423.01 provides guidance on using ambiguity symbols in nucleotide sequences:

“For those nucleotides that are ambiguous in designation, the list of one-letter codes given in WIPO Standard ST.25 (1998), Appendix 2, Table 2, must be used.”

Some common ambiguity symbols include:

• n – a or c or g or t/u
• r – a or g (purine)
• y – c or t/u (pyrimidine)
• k – g or t/u
• m – a or c

These symbols allow for the representation of positions where multiple nucleotides are possible. It’s crucial to use these standardized symbols to ensure clarity and consistency in sequence listings.