Ambiguous nucleotide
Ambiguous nucleotides are used when the true nucleotide is unknown. The most popular one seen with high-throughput genome sequences is "N" which represents any possible nucleotide.
Nucleotide Code Adenosine A Cytidine C Guanine G Thymidine T Uridine (if 'Alphabet' set to 'RNA') U Purine (A or G) R Pyrimidine (T or C) Y Keto (G or T) K Amino (A or C) M Strong interaction (3 H bonds) (G or C) S Weak interaction (2 H bonds) (A or T) W Not A (C or G or T) B Not C (A or G or T) D Not G (A or C or T) H Not T or U (A or C or G) V Any nucleotide (A or C or G or T or U) N