An interplay between compositional constraint and natural selection dictates the codon usage pattern among select...

Galliformes are believed to be the first avian order that started living in human association and became domesticated. Members of this order ranged from common to rare species. Next-generation sequencing has availed researchers with the whole genome sequences of five Galliformes; chicken, helmeted Guinea fowl, turkey, Japanese quail, and peafowl. Bioinformatic analysis based on codon usage, evolution, and species-specific functional enrichment can provide some crucial information aiding proper understanding of their genomic strategies. In this study, we investigated the genomic features of chicken, helmeted guinea fowl, turkey, and Japanese quail. Their genomes were AT biased although the potentially highly expressed genes contained more GC than AT. Cytosine dominated the third position of frequently used optimal codons. Mutational pressures in the analyzed Galliformes were in the range of 0.2-0.6%. Neutrality plot, translational selection index, and mutational responsive index indicated the dominance of selection pressure over mutational pressure among Galliformes. A pair of di-nucleotides, TpA and CpG, was found to be used less frequently than others in protein-coding genes since both of them are associated with the conversion of euchromatin to heterochromatin. Functional enrichment analysis revealed the dominance of proteins associated with fundamental biological processes. In turkey, chicken and helmeted Guinea fowl proteins with immunity-boosting capacity prevailed along with proteins needed for signal transduction and maintenance of central dogma. Evolutionary analysis indicated a bias towards synonymous substitution than non-synonymous mutation.