IUB ambiguity codes

Symbols used for describing an oligonucleotide sequence are

A = adenosine

(for the nucleoside - the base is adenine, the nucleotide is adenylic acid)

C = cytidine

(for the nucleoside - the base is cytosine, the nucleotide is cytidylic acid)

G = guanosine

(for the nucleoside - the base is guanine, the nucleotide is guanylic acid)

T = thymidine

(for the nucleoside - the base is thymine, the nucleotide is thymidylic acid)

Symbols for describing mixed base position in an oligonucleotide sequence (ambiguity codes) are

R = A + G	Y = C + T	K = G + T
M = A + C	S = C + G
W = A + T

V = A + C + G	B = C + G + T 	
H = A + C + T		
D = A + G + T

N = A + G + C + T

An additional symbol often used for describing an oligonucleotide sequence

I = inosine

(or hypoxanthosine for the nucleoside - the base is hypoxanthine, the nucleotide is inosinic acid)