IUPAC codes

The International Union of Pure and Applied Chemistry (IUPAC) has defined a standard representation of DNA bases by single characters that specify either a single base (e.g. G for guanine, A for adenine) or a set of bases (e.g. R for either G or A). UCSC uses these single character codes to represent multiple observed alleles of single-base polymorphisms.

Symbol Bases Origin of designation
G G Guanine
A A Adenine
T T Thymine
C C Cytosine
R G or A puRine
Y T or C pYrimidine
M A or C aMino
K G or T Keto
S G or C Strong interaction (3 H bonds)
W A or T Weak interaction (2 H bonds)
H A or C or T not-G, H follows G in the alphabet
B G or T or C not-A, B follows A
V G or C or A not-T (not-U), V follows U
D G or A or T not-C, D follows C
N G or A or T or C aNy