Question

How can you use synonymous and non-synonymous mutations to distinguish drift, purifying selection and positive selection from one another?

Answer 1

Answer - Some of these mutations are minor and do not change anything. These DNA mutations are called synonymous mutations. Others can change the gene that is expressed and the phenotype of the individual.Mutations that do change the amino acid, and usually the protein, are called nonsynonymous mutations .The neutral theory tells us that synonymous substitutions will be tolerated, but nonsynonymous substitutions will be removed by purifying selection. Therefore, nonsynonymous substitutions will be fewer than synonymous substitutions. The synonymous substitutions typically exceed nonsynonymous substitutions in protein-coding genes, and functionally constrained regions of genes evolve at a slower rate than regions that are not functionally constrained. However, if a nonsynonymous substitution confers some selective advantage, then it will be rapidly fixed in the population by positive selection.