On December 21, 2021, Brian R. Morton, professor of biological sciences, published new research in the Journal of Molecular Evolution titled “Context-Dependent Mutation Dynamics, Not Selection, Explains the Codon Usage Bias of Most Angiosperm Chloroplast Genes.” This latest article on how natural selection influences the genes that control photosynthesis in flowering plants builds on his previous discovery that selective constraints have acted on the psbA gene, causing codon adaptation. (A codon is a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule.) In the previous study, he and his fellow researchers also looked at three other chloroplast genes and found results that were in alignment with predictions based on their evolution simulations.
Morton’s research for the Journal of Molecular Evolution examines two competing proposals about the degree to which natural selection affects codon usage of angiosperm chloroplast genes. The first proposal is that selection plays a significant role with widespread changes. The second proposal is that selection influences only one or two highly expressed genes. Morton found support for the second proposal: Natural selection does not appear to be a widespread factor in changes to codon usage by angiosperm chloroplast genes. He concludes the article by encouraging the use of caution when analyzing composition data and highlighting the need for a rigorous analysis of mutation dynamics.