|  | 
	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 |  |  |