A gene has 300 non synonymous sites and 150 synonymous sites. The synonymous sites have mutation rate 6.0 × 10-7/yr, while non synonymous sites have mutation rate 3.0 × 10-9/yr. What is the expected number of mutations of each type after 2 million years? What is the probability of no mutations of either type?
In most genes, mutations in some sites ("synonymous sites") have no effect on the protein produced, while those in other sites ("non synonymous sites") do affect the protein. In general, mutation rates are higher in synonymous sites because changes are not removed by natural selection.