Transition-transversion mutations in the polyketide synthase gene of Aspergillus section Nigri

This study determined the transition-transversion mutation in the pks gene of Aspergillus section Nigri in order to gain insight into the patterns of nucleotide base substitution and the process of molecular evolution using standard recommended techniques. Results obtained depict frequent occurrence of transition (23 +/- 0.96) than transversion (11.37 +/- 1.38) (p < 0.05) with C/T being the most frequently observed transitional base substitution and C/A the most frequently occurring transversional base change. The number of single base insertions (56 +/- 1.00) were significantly higher than the observed single base deletions (38 +/- 2.00) (p < 0.05) while varying degrees of two or more base deletions and insertions were also observed both inside and outside the open reading frame. The maximum likelihood value estimated for the pks gene was calculated to be -9458.80 in 423 positions of the final dataset while the transition-transversion ratio was estimated to be 0.50. The Tajima's neutrality test approaches seven (7) with the nucleotide diversity estimated to be approximately 65%. Evolutionary test depicts positive selection as ratio of non synonymous to synonymous divergence was found to be greater than ratio of the number of non synonymous to synonymous polymorphisms. The proportion of substitution driven by positive selection was calculated to be approximately 96.2%. This research therefore provides an insight into the understanding of pks gene mutation patterns as some of the observed indels resulted in frame shift mutations.