s Number of synonymous sites
n Number of nonsynonymous sites
S Number of synonymous substitutions
N Number of synonymous sites
dS Synonymous substitution rate
dN Nonsynonymous substitution rate
dN/dS Selective strength of sequence
t Divergence time between two sequences
tr Transition /transversion ratio
dN-dS Difference in numbers of nonsynonymous and synonymous substitutions per site
  (p-distance)
P Probability of rejecting the null hypothesis of neutral evolution
Table 1: Symbols and abbreviation used for synonymous and non synonymous substitution used in Molecular evolutionary genetic analysis software.