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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 |
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