IUPAC nucleotide ambiguity codes

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Symbol       Meaning      Nucleic Acid
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A            A           Adenine
C            C           Cytosine
G            G           Guanine
T            T           Thymine
U            U           Uracil
M          A or C
R          A or G
W          A or T
S          C or G
Y          C or T
K          G or T
V        A or C or G
H        A or C or T
D        A or G or T
B        C or G or T
X      G or A or T or C
N      G or A or T or C
	

Reference:

IUPAC-IUB SYMBOLS FOR NUCLEOTIDE NOMENCLATURE:
Cornish-Bowden (1985) Nucl. Acids Res. 13: 3021-3030.