Table 1 Notation

A

Adenine content

T

Thymine content

G

Guanine content

C

Cytosine content

GC

Guanine-plus-cytosine content, GC = G + C

S

Guanine-plus-cytosine content, S = G + C

R

Purine (adenine-plus-guanine) content, R = A + G

A _i

Adenine content at codon position i, i = 1, 2, 3

T _i

Thymine content at codon position i, i = 1, 2, 3

G _i

Guanine content at codon position i, i = 1, 2, 3

C _i

Cytosine content at codon position i, i = 1, 2, 3

S _i

Guanine-plus-cytosine at codon position i, S _i = G _i + C _i , i = 1, 2, 3

R _i

Purine content at codon position i, R _i = A _i + G _i , i = 1, 2, 3