Final Answer:
Mutations in synonymous sites accumulate faster because most if not all are neutral while most mutations at nonsynonymous sites are removed by purifying or normalizing selection is the best explanation for the differences between the rate of change in nonsynonymous compared to synonymous sites. Therefore, the correct option is B) Mutations in synonymous sites accumulate faster because most if not all are neutral while most mutations at nonsynonymous sites are removed by purifying or normalizing selection.
Step-by-step explanation:
The differences in the rate of change between nonsynonymous and synonymous sites primarily stem from selection pressures. Option B is the best explanation: mutations in synonymous sites accumulate faster as they are mostly neutral, not affecting the encoded protein's structure or function.
Consequently, they are less likely to be removed by selection. In contrast, nonsynonymous mutations impact the protein sequence and are often deleterious, resulting in their removal by purifying selection, which eliminates harmful genetic variations. This phenomenon leads to a slower accumulation of mutations in nonsynonymous sites.
The disparity in evolutionary rates between these sites reflects the contrasting selective forces acting upon neutral and functional genomic elements, shaping genetic diversity within populations and species. Therefore, the correct option is B) Mutations in synonymous sites accumulate faster because most if not all are neutral while most mutations at nonsynonymous sites are removed by purifying or normalizing selection.
The complete question is "Looking at the above chart, which of the following is the best explanation for the differences between the rate of change in nonsynonymous compared to synonymous sites? A) Most mutations at synonymous sites increase overall fitness and are favored by positive selection, whereas most mutations at nonsynonmous sites are deleterious and are selected against. B) Mutations in synonymous sites accumulate faster because most if not all are neutral while most mutations at nonsynonymous sites are removed by purifying or normalizing selection C) Fixation rates should be equal to mutation rates so the mutation rates at synonymous sites must differ from those at nonsynonymous sites. D) Mutations at synonymous sites are more likely to generate stable polymorphisms than those at nonsynonymous sites."