Effective number of codon (Nc) can be calculated from the codon data alone and it is independent of gene or its length. Codon W 1.4.2 was used to calculate Nc and the correlation between the percentages of GC3 (frequency of G+C at third position). Genes with large Nc have smaller codon preferences (Wright, 1990).where, X is mole percent of alanine (A), valine (V), isoleucine (I) and leucine (L). The numerical value of a, and b are 2.9 and 3.9, which is the relative volumes for V and L/I side chain, respectively