nucleotide degenercy code

ref: http://www.le.ac.uk/bl/phh4/nucredun.htm

A = Adenine

C = Cytosine

T = Thymine

G = Guanine

U = Uracil

N = A, G, C or T = aNy

R = A or G = puRine (9-ring with 4 N and 5 C)

Y = C or T (also U) = pYrimidine (6-ring with N at positions 1 and 3)

M = A or C = aroMatic

S =  G or C 

W = A or T 

 K = G or T = Keto 

V = A, C or G = Not T (letter after)

D = A, G or T = Not C

H = A, C or T = Not G

B = C, G or T = Not A