2.2. Sequence compositional features
Calculating the base content (totally and in each position for all codons) in percent, GC content (totally and GC1, 2, 3) in percent, number of codons and their frequencies and synonymous codon usage features – the percentage of each synonymous codon in each codon family that codes for the same amino acid –was donewith FREQSQ program (http://www.bioinfo.hku.hk). Also, for estimating the codon usage bias for each gene, codon adaptation index (CAI) was assessed for each gene (http://genomes.urv.es/CAIcal/).